Dr. Masters’ Tropical Watch

Norbert Hits Category 3; Three Minor Atlantic Threat Areas to Watch

By: Jeff Masters , 4:13 PM GMT on September 06, 2014

Hurricane Norbert put on an unexpected burst of rapid intensification overnight, topping out as a Category 3 storm with 120 mph winds at 5 am EDT Saturday. Norbert continues to chug parallel and just offshore from the coast of Mexico’s Baja Peninsula, bringing heavy rain and tropical storm-force winds to the coast. Satellite loops on Saturday morning showed that Norbert had a small eye and some very impressive eyewall thunderstorms with cold cloud tops. However, the storm is starting to weaken, thanks to cooler ocean temperatures near 27°C (81 °F), and drier air. The models all show the core of the hurricane remaining just offshore as it moves northwest parallel to the Baja Peninsula over the next three days, so heavy rains of 3 – 6″ causing flash flooding will be the primary threat from Norbert to Baja. The counter-clockwise flow of air around the hurricane is pulling moisture from the remnants of Tropical Storm Dolly and from the tropical Eastern Pacific northwards into Northern Mexico and the Southern Arizona, and this moisture will be capable of causing flooding rains in those regions.

Norbert’s intensification into a Category 3 storm gives the Eastern Pacific seven major hurricanes so far this year. With the season typically only 2/3 over by September 9, we have a decent chance of tying or beating the record of ten intense hurricanes in a season, set in 1992 (this tally includes hurricanes in the Central Pacific.) The 2014 tally for the Eastern Pacific currently stands at 14 named storms, 10 hurricanes, and 7 intense hurricanes. An average Eastern Pacific hurricane season sees 15 named storms, 8 hurricanes, and 3 intense hurricanes during the entire year. The records for total number of named storms, hurricanes, and intense hurricanes were all set in 1992, with 28 named storms, 16 hurricanes, and 10 intense hurricanes (with the Central Pacific tallies included.)

Figure 1. Hurricane Norbert near Mexico’s Baja Peninsula at 10:30 am EDT September 6, 2014. At the time, Norbert was a Category 3 storm with 115 mph winds. Image credit: NASA/GSFC.

Figure 2. Predicted seven-day precipitation amounts for the period ending on Saturday, September 13 show a large area of 3+ inches are expected over Southeast U.S., thanks to a weak tropical disturbance. A region of 2+” of rain is expected over Southern Arizona due to the flow of moist air northwards caused by Hurricane Norbert’s circulation. Image credit: NOAA/HPC.

Southeast U.S. disturbance bringing heavy rains
A weak area of low pressure near the coast of Georgia is bringing heavy rain showers to the Southeast U.S. coast and adjacent waters, but this this activity is very disorganized. The disturbance will bring heavy rains in excess of three inches to the coast over the next few days as the low drifts northeastward. After that time, the low will likely merge with a frontal zone over the ocean and head out to sea. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odd of development odds of 0% and 10%, respectively.

Tropical Wave 90L
A tropical wave (90L) located a few hundred miles west of the Cape Verde Islands is headed west to west-northwest at about 15 mph. Satellite images show 90L has plenty of spin, but little heavy thunderstorm activity. Though Sea Surface Temperatures are fairly warm, 27.5°C (82°F), and wind shear is low, 90L is embedded in a very dry air mass that is expected to get dryer as the storm progresses westwards. None of our three reliable computer models for predicting tropical storm formation predicts development of 90L over the next five days. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odd of development odds of 10%. The wave should arrive in the northern Lesser Antilles Islands by Wednesday night.

New African Tropical Wave
Following on the heels of 90L will be a new tropical wave that is expected to push off the coast of Africa on Sunday night or Monday morning, bringing heavy rain showers and gusty winds to the Cape Verde Islands on Monday and Tuesday. All three of our three reliable computer models for predicting tropical storm formation show development of the new wave by Wednesday. The new wave will see similar conditions to 90L, though, and will struggle with dry air and moderate wind shear. In their 8 am EDT Saturday Tropical Weather Outlook, NHC gave the system 2-day and 5-day odd of development odds of 0% and 30%, respectively. The wave should take a more northwesterly track then 90L, and not threaten the Lesser Antilles Islands.

from:    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2788

Dr. Masters on Tropical Storms

Cristobal a Hurricane; Little Change to 97L

By: Dr. Jeff Masters , 12:25 PM GMT on August 26, 2014

It doesn’t look much like hurricane, but the Hurricane Hunters measured surface winds around 75 mph on Monday evening and Tuesday morning in Hurricane Cristobal, making it the third hurricane of the 2014 Atlantic hurricane season. These missions proved the value of hurricane hunter flights, since there is no way that we would have known Cristobal was a hurricane based on satellite data. The storm is stretched out in a long line of heavy thunderstorms, has no eye or low-level spiral bands, and is giving early August’s Hurricane Bertha some stiff competition for ugliest Atlantic hurricane of the century. Along with Hurricane Arthur and Hurricane Bertha, Cristobal gives us three Atlantic hurricanes so far this year, exceeding the entire 2013 Atlantic hurricane season total. The second (and final) hurricane of the 2013 season (Ingrid) did not arrive until September 14. On average, the third hurricane of the Atlantic season arrives on September 9, and the third named storm of the year on August 13. The last time the first three named storms in the Atlantic became hurricanes was in 1983, when Alicia, Barry and Chantal all became hurricanes (if we exclude 1992, when an unnamed subtropical storm formed prior to the arrival of Hurricanes Andrew, Bonnie, and Charley.) Cristobal continues to dump heavy rains over the Central and Southeast Bahamas and Turks and Caicos Islands as the storm heads northeastwards out to sea. Satellite loops show that Cristobal is struggling with wind shear, with a center of circulation partially exposed to view, and all the heavy thunderstorms pushed to the south and east sides of the center. The only land area at risk from Cristobal is Bermuda, and the 5 am EDT Tuesday Wind Probability Forecast from NHC gave that island a 27% chance of experiencing tropical storm force winds of 39+ mph. The GOES-14 satellite is in rapid-scan mode over Cristobal on Tuesday, and you can access an impressive 1-minute resolution satellite loop of the storm from the NOAA/RAMMB website.

Figure 1. MODIS true-color image showing Tropical Storm Cristobal’s intense thunderstorms stretching from the Southeast Bahamas to Bermuda at 2 pm EDT on August 25, 2014. At the time, Cristobal had top winds of 60 mph. Image credit: NASA.

Little change to 97L headed towards the Lesser Antilles
A tropical wave (Invest 97L) was near 13°N, 47°W on Tuesday morning, about 900 miles east of the Lesser Antilles Islands, and was headed west to west-northwest at about 15 mph. Satellite loops show the wave has changed little since Monday, and has a modest amount of spin but only a small amount of heavy thunderstorms. Water vapor satellite images and the Saharan Air Layer analysis show that 97L is located in a dry environment, which is keeping development slow. Wind shear was a moderate 10 – 20 knots, which should allow some slow development. Sea Surface Temperatures are near 27.5°C, which is warm enough to allow some slow development. The wave should arrive in the Lesser Antilles Islands by Friday and be near Puerto Rico on Saturday, according to the Tuesday morning runs of the GFS model. None of the three reliable computer models for predicting tropical storm formation predict 97L will develop over the next five days. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 97L 2-day and 5-day development odds of 0% and 20%, respectively. These odds are 10% lower than their previous advisory, and NHC has stopped running their suite of models on 97L.

New tropical wave coming off coast of Africa this weekend
A large and powerful tropical wave will move off the coast of Africa on Friday evening, and the GFS model has been very aggressive in recent runs about developing this wave into a tropical storm within a day of its emergence. The other reliable models for tropical cyclone genesis, the European and UKMET models, have not been developing this wave right away. Residents of the Cape Verde Islands should anticipate the possibility of heavy rain and strong winds on Saturday as the wave moves west at 10 – 15 mph across the islands. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 97L 2-day and 5-day development odds of 0% and 30%, respectively.

The Gulf of Mexico is worth watching
In the Gulf of Mexico, heavy thunderstorm activity has diminished since Monday along a weak cold front stretching from South Florida to the Louisiana coastal waters. Some models show a weak area of low pressure developing along this front and moving westwards over Texas by Friday, and we should keep an eye on this region for development.

Figure 2. MODIS true-color image of Hurricane Marie in the Eastern Pacific taken at approximately 18:15 UTC (2:15 pm EDT) on August 25, 2014. At the time, Marie was a Category 4 storm with 145 mph winds. Image credit: NASA.

Powerful Hurricane Marie generating huge waves in Eastern Pacific
The Eastern Pacific’s Hurricane Marie had weakened to a Category 2 storm with 105 mph winds on Tuesday morning, but was still generating huge swells that were bringing large waves to the coasts of Southern California and Mexico’s Baja Peninsula. At 5 am EDT on Tuesday, Marie’s tropical storm-force winds covered a huge area of ocean, up to 275 miles from the center, and 12-foot high seas extended up to 550 miles from the center. A High Surf Advisory is in effect for Los Angeles, where waves of 10 – 15 feet will potentially cause structural damage to piers and beachside property as well as significant beach erosion. The powerful surf will be accompanied by strong rip currents and long-shore currents, making for very hazardous swimming and surfing conditions through Thursday. Satellite loops on Tuesday morning showed a steady degradation of Marie’s cloud pattern, with the eyewall cloud tops warming and the areal coverage of the strongest thunderstorms decreasing. The storm is headed to the northwest over cooler waters and into drier air, and will not affect any land areas.

You can see a spectacular loop of infrared satellite images of Marie as it intensified into a Category 5 storm on Sunday at the CIMSS University of Wisconsin.

from:    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2776

Dr. Jeff Masters on Tornadoes and Cyclones

By: Dr. Jeff Masters, 2:55 AM GMT on January 13, 2014 +39

The year 2014 has just begun, but the tropical cyclone seasons in both the Northern and Southern Hemispheres have already claimed victims. Summer is in full bloom in the Southern Hemisphere, where two Category 4 storms formed last week: Tropical Cyclone Colin, which reached sustained winds of 135 mph midway between Madagascar and Australia on January 11, and Tropical Cyclone Ian, which intensified into a powerful Category 4 storm with 145 mph winds before roaring through the South Pacific islands of Tonga over the weekend. At least one death is being blamed on the storm in the northern Ha’apai Islands of Tonga, home to 8,000 people, and 70% of the buildings were damaged or destroyed, according to the Australia Network News. Tonga is an archipelago of 176 islands, with 100,000 people living on the 36 most populated islands. The economy relies on fish exports, tourism, and money from Tongans living overseas. About 40% of the population lives in poverty.

In the Philippines, heavy rains from tropical disturbance 91W have triggered flash floods and mudslides that are being blamed for six deaths on the southern island of Mindanao on Saturday, with eight other people missing. Twenty-four hour rainfall amounts in excess of 300 mm (11.81″) fell in northeast Mindanao, according to Project NOAH. The disturbance will move slowly north over the islands through Tuesday, and bring torrential rains in excess of 5″ to the islands of Leyte and Samar, ravaged by Super Typhoon Haiyan in November.

Figure 1. MODIS image of Tropical Cyclone Ian as its eye passed over Tonga at approximately 00 UTC on January 11, 2014. At the time, Ian was a Category 4 storm with winds of 145 mph. Image credit: NASA.

First U.S. Tornadoes of 2014 hit Virginia and Georgia
A modest severe weather outbreak over the Southeast U.S. on Saturday, January 11, brought the first tornadoes of 2014: three to Virginia, and one to Georgia:

1. EF-0 tornado near Waleska in Cherokee Co, GA, 3 mile path length, downed trees, damaged fence.

2. EF-0 in Isle of Wight Co., VA, 70-75 mph, 2 mile path, 50 yards wide, trees down, roof damage to homes, no injuries.

3. EF-0 near Smithfield, VA, EF-0, 75-80 mph, 1.4 mile path, 100 yards wide, trees down onto homes, no injuries.

4. EF-0 tornado in Hampton, VA, 80 mph, 1.25 mile path, 75 yards wide; trees snapped, shingles off homes, roof off City of Hampton school maintenance compound; Fox Hill Athletic Association building destroyed.

The strongest wind gust ever recorded at Raleigh-Durham International Airport, 86 mph, occurred at 1:57 PM Saturday, when a line of thunderstorms roared through central North Carolina.

from:    http://www.wunderground.com/blog/JeffMasters/show.html

Tropical Storm Karen

Hurricane Watches are flying along the U.S. Gulf Coast as Tropical Storm Karen heads north-northwest into the Gulf of Mexico. Karen, the eleventh named storm of the 2013 Atlantic hurricane season, formed about 8 am EDT Thursday in the Southeast Gulf of Mexico. It’s not often that one sees a new storm start out with 60 mph sustained winds, but that’s what an Air Force hurricane hunter plane found this morning near 7:30 am EDT, when they sampled the northern portion of the storm. A ship located about 50 miles northeast of the northeast tip of the Yucatan Peninsula measured sustained winds of 51 mph near the same time. Satellite loops show that Karen is a medium-sized storm with an area of very intense thunderstorms along its northern and eastern flanks. Wind shear has risen since Wednesday, and is now a moderately high 20 knots, thanks to strong upper-level winds out of the west-southwest. These strong winds are keeping any heavy thunderstorms from developing on the west side of Karen’s center of circulation, by driving dry air that is over the Yucatan Peninsula and Western Gulf of Mexico into Karen’s core. As a result, Karen has a lopsided comma-shape on satellite imagery. Karen has a strong upper-level outflow channel to its north that is helping ventilate the storm, though, and ocean temperatures are a very warm 29°C (84°F). Between 7 am and 9:30 am EDT the Hurricane Hunters made three passes though the center of Karen, and the central pressure stayed roughly constant at 1004 mb, so Karen is not undergoing much change.
Figure 1. Odds of receiving more than 4″ of rain over a five-day period beginning at 2 am EDT Thursday October 3, 2013, as predicted by the experimental GFDL ensemble model.

Forecast for Karen
Wind shear will steadily increase as the storm heads north-northwest, and shear will reach a high 25 knots by Saturday morning as Karen closes in on the U.S. Gulf Coast, according to the latest SHIPS model forecast. The atmosphere will grow drier as Karen moves into the Northern Gulf of Mexico, and the drier air combined with increasing wind shear will retard development, making only slow intensification likely through Friday. A trough of low pressure and an associated cold front will be moving through Louisiana on Saturday, and the associated upper-level westerly winds will be able to turn Karen more to the northeast as it approaches the coast on Friday evening and Saturday morning. The higher shear at that time should be able to induce weakening, and the 8 am EDT Thursday wind probability forecast from NHC gave a 28% chance Karen will be a hurricane at 2 am EDT Saturday, down from 44% on Friday afternoon. Most of the models predict landfall will occur along the western Florida Panhandle Saturday afternoon or evening. The usually reliable European model has Karen making landfall over Eastern Louisiana, though. If Karen does follow this more westerly path, the storm will be weaker, since there is more dry air and higher wind shear to the west. Since almost all of Karen’s heavy thunderstorms will be displaced to the east by high wind shear, there will be relatively low rainfall totals of 1 – 3″ to the immediate west of where the center makes landfall. Much higher rainfall totals of 4 – 8″ can be expected to the east. To judge the possibilities of receiving tropical storm-force winds at your location, I recommend using the NHC wind probability forecast. The highest odds of tropical storm-force winds (45 – 55%) are along the coast from Buras, Louisiana, to Pensacola, Florida.
Read more at http://www.wunderground.com/blog/JeffMasters/show.html#UbifOgDIGFGEKfq7.99

TS Dorian Making a Comeback?

After a long trek over the Atlantic Ocean from the coast of Africa, the remains of Tropical Storm Dorian (now called Invest 91L) have finally arrived at the shores of North America. Ex-Dorian is nearly stationary, and is situated over the Northwestern Bahama Islands, just off the coast of Southeast Florida. Satellite loops and Melbourne, Florida radar images show that ex-Dorian has only a limited amount of heavy thunderstorms, which are not well-organized. There does appear to be a surface circulation center trying to form just north of the storm’s heaviest thunderstorms, about 70 miles east of Vero Beach, Florida. However, dry air to the northwest, as seen on water vapor satellite loops, is inhibiting development. WInd shear is moderate, 10 – 20 knots, but is expected to rise to the high range, 20 – 30 knots, by Saturday morning. Ex-Dorian is expected to move slowly northwards and then north-northeastwards on Saturday. This motion will get ex-Dorian tangled up with a cold front that extends from Northern Florida northeastwards, just offshore from the Southeast U.S. coast. Before it merges with the front, ex-Dorian has some potential for regeneration into a tropical depression, and in their 8 am Friday Tropical Weather Outlook, NHC gave ex-Dorian a 30% chance of becoming a tropical cyclone by Sunday. Ex-Dorian will likely bring heavy rains to the Northwest Bahamas on Friday, and these heavy rains may also clip the coast of Southeast Florida. However, the bulk of ex-Dorian’s rains should stay offshore.

Figure 1. Morning radar image of ex-Dorian from the Miami radar.

from:    http://www.wunderground.com/blog/JeffMasters/show.html

Dr. Jeff Masters on TR Chantal

Tropical Storm Chantal is strengthening as it speeds west-northwestwards at 26 mph through the Lesser Antilles Islands. At 6:22 am AST, St. Lucia recorded a wind gust of 54 mph. Sustained winds of 38 mph, gusting to 52 mph, were observed at Martinique at 10 am AST. An Air Force hurricane hunter aircraft is in the storm, and measured top winds at their 1,000′ flight level of 80 mph at 8:41 am AST, about 20 miles north of the center. Top winds seen by the aircraft’s SFMR instrument were about 60 mph, and it is likely that NHC will bump up Chantal’s top winds to at least 60 mph in their 11 am advisory. Barbados Radar shows a large area of heavy rain that has organized moderately well into low-level spiral bands affecting much of the central Lesser Antilles Islands. Chantal is not very impressive on satellite loops, though, with only a modest amount of heavy thunderstorms that are not well-organized. Only a small amount of upper-level outflow is visible. Chantal is fighting dry air associated with the Saharan Air Layer (SAL), as seen on water vapor satellite loops. Moderate wind shear of 15 – 20 knots is driving dry air into the storm. Ocean temperatures are fairly warm, at 28°C.

Figure 1. Latest satellite image of Chantal.

Figure 2. Barbados weather radar image of Chantal taken at 9:14 am AST on Tuesday, July 9, 2013. Chantal’s center was located between St. Lucia and Martinique. Image credit: Barbados Met Service.

Forecast for Chantal
Chantal will likely continue to intensify before hitting Hispaniola on Wednesday afternoon. In their 5 am EDT wind probability forecast, NHC gave Chantal a 23% chance of becoming a hurricane before hitting Hispaniola. Working against intensification will be the fast forward speed of the storm–tropical storms moving faster than 20 mph in the deep tropics usually have trouble intensifying. In addition, the Eastern Caribbean is an area where the trade winds accelerate, helping drive sinking air that discourages tropical storm intensification. Dry air will also slow down the intensification process. Interaction with the high mountains of Hispaniola and high wind shear may be able to destroy Chantal by Thursday. The 8 am EDT Tuesday wind shear forecast from the SHIPS model calls for shear to rise to the high range, 20 – 30 knots, as the storm approaches and crosses Hispaniola on Wednesday and Thursday. On Friday and Saturday, when Chantal is expected to be in the Bahamas, lower moderate wind shear of 15 – 20 knots should allow for re-intensification of the storm–if it survives interaction with the high mountains of Hispaniola, Puerto Rico, and Eastern Cuba. The latest 06Z run of the GFS model dissipates Chantal as it crosses Hispaniola, though the 00Z run done 6 hours earlier had the storm surviving. Chantal has the potential to cause big problems for Haiti, which is highly vulnerable to flash flooding due to the lack of vegetation on the deforested mountains. However, there is a lot of dry air to the west of Chantal, which may act to keep rainfall totals in Haiti down to a manageable 2 – 4″. Over 300,000 people are still homeless and living in makeshift tent camps in Haiti, three years after the great 2010 earthquake.

Chantal’s fast west-northwest forward speed of 26 mph will slow to 20 mph by Wednesday afternoon and then 10 mph by Thursday afternoon, as the storm “feels” the presence of a trough of low pressure over the U.S. East Coast. This trough will steer Chantal to the northwest and then north-northwest across Hispaniola and into the Bahamas. The trough of low pressure pulling Chantal northwards is expected to lift out the the northeast over the weekend, leaving Chantal behind off the coast of Florida. High pressure will likely build in, potentially forcing an intensifying Chantal westwards into the Florida or Southeast U.S. coast, with a possible Monday landfall.

from:      http://www.wunderground.com/blog/JeffMasters/show.html

Tropical Storm Andrea Forms in Gulf

The Atlantic has its first named storm of the 2013 hurricane season: Tropical Storm Andrea. An Air Force hurricane hunter plane was able to locate a closed center of circulation, and found surface winds of 40 mph in the large area of thunderstorms on the east side of the center. Satellite loops show that Andrea is a lopsided storm. It’s center of circulation is exposed to view, due to a large region of dry air that covers the entire Central and Western Gulf of Mexico. This dry air is from a trough of low pressure whose upper level winds are also creating moderate wind shear of 15 – 20 knots over Andrea. Wind shear is forecast to rise to the high range, 20 – 40 knots, by Thursday. Andrea is forecast to make landfall along the northern Gulf Coast of Florida by Thursday evening, so the system has a short window of time to intensify. Given the large amount of dry air to Andrea’s west, and the forecast for increasing shear up until landfall, I expect that the strongest sustained winds Andrea could have before landfall are 50 mph. Heavy rains will be the storm’s main threat, though a few isolated EF-0 tornadoes will also be possible in some of the heavier thunderstorms in Andrea’s spiral bands. A storm surge of 2 – 4 feet is predicted for Tampa Bay northward to Apalachicola, and rip currents will be a risk for swimmers who brave the high surf. Fort Pickens, located in Gulf Islands National Seashore on a barrier island offshore from Pensacola, Florida, has been closed to visitors due to the approaching storm. A single 2-lane road vulnerable to storm surges runs to Fort Pickens. Officials want to prevent a repeat of the situation that occurred in September 2011, when Tropical Storm Lee pushed a storm surge over the road that blocked it with sand and debris, trapping numerous campers and visitors in Fort Pickens. As of 7 pm EDT, our wundermap with the storm surge layer turned on was showing storm surge levels were less than 1 foot along the Florida coast.

Figure 1. MODIS image of Tropical Storm Andrea in its formative stages, taken at 12:20 pm EDT Wednesday, June 5, 2013, five hours before it was named. Image credit: NASA.

Andrea’s place in history
Andrea formed in a typical location for early-season storms. The Gulf of Mexico, Western Caribbean, and Bahamas are the usual areas for the genesis of June tropical storms. Andrea’s formation date of June 5 is over a month earlier than the average July 9 date for formation of the season’s first named storm. On average, the Atlantic sees one June named storm every two years. In 2012, we’d already had two named storms by this point in the season–Alberto and Beryl. This year is the second time a storm named Andrea has appeared in the Atlantic. The previous incarnation, Subtropical Storm Andrea of 2007, wandered off the U.S. East Coast in May, and never made landfall. The 2013 version of Andrea is highly unlikely to get its name retired, and we’ll be seeing a third coming of the storm in 2019.

from:    http://www.wunderground.com/blog/JeffMasters/show.html

Dr. Jeff Masters on Nadine, New Tropical Depression

TD 15 forms; tropical storm warnings in the Azores for Nadine

Published: 4:12 PM GMT on October 03, 2012
The first new tropical depression in the Atlantic since September 11 is here, Tropical Depression Fifteen. TD 15 is destined for a short life, though, and will not be a threat to any land areas. The storm is already showing signs that moderate wind shear of 10 – 20 knots is interfering with development, with most of the storm’s heavy thunderstorms displaced away from the center of circulation. Wind shear is expected to rise to the high range, above 20 knots, on Thursday and Friday as the storm turns north and then northeast. Ocean temperatures will cool from 28°C today to 25°C by Saturday, and all of the computer models show TD 15 ceasing to exist by Saturday, as the storm becomes absorbed by a large extratropical storm. TD 15 is a classic example of a weak, short-lived tropical cyclone that would have gotten missed before satellites came around. If TD 15 strengthens, it will be called Tropical Storm Oscar.

Figure 1. MODIS satellite image of TD 15 taken at 8:52 am EDT Wednesday, October 3, 2012. At the time, TD 15 was just forming and had top winds of 35 mph. Image credit: Navy Research Lab, Monterey.

Nadine touring the Azores Islands–again
I’m-not-dead-yet Tropical Storm Nadine is back for a second tour of the Azores Islands, where tropical storm warnings are up for the storm’s expected arrival tonight. Nadine is struggling with cool 21 – 22°C waters and high wind shear of 20 – 30 knots, and could transition to an extratropical storm later today or on Thursday as it heads east at 14 mph. Nadine is up to 21 days as a tropical or subtropical cyclone as of 2 pm today, making it the fifth longest-lived Atlantic tropical cyclone of all-time (tropical cyclones include tropical depressions, tropical storms, and hurricanes, but not extratropical storms.) According to the official HURDAT Atlantic database, which goes back to 1851, only five previous Atlantic tropical cyclones have lasted 21 days or longer (thanks go to Brian McNoldy for these stats):

1) San Ciriaco Hurricane of 1899: 28 days
2) Ginger, 1971: 27.25 days
3) Inga, 1969: 24.75 days
4) Kyle, 2002: 22 days
5) Nadine, 2012: 21 days
5) Hurricane Four, 1926: 21 days

According to the Hurricane FAQ, the all-time world record is held by Hurricane John in the Eastern Pacific, which lasted 31 days as it traveled both the Northeast and Northwest Pacific basins during August and September 1994. (It formed in the Northeast Pacific, reached hurricane force there, moved across the dateline and was renamed Typhoon John, and then finally recurved back across the dateline and renamed Hurricane John again.) Of course, there may have been some longer-lived storms prior to 1961 that we didn’t observe, due to the lack of satellite data.

Figure 2. MODIS satellite image of Hurricane Nadine taken at 8:45 am EDT Wednesday, October 3, 2012. At the time, Nadine had top winds of 50 mph. Image credit: NASA.

Jeff Masters

from:    http://www.wunderground.com/blog/JeffMasters/article.html?entrynum=2248

Jeff Masters on Current ATlantic Tropical Activity

Isaac pounding Louisiana, Mississippi, Alabama, and Florida

Published: 4:01 PM GMT on August 29, 2012
Hurricane Isaac continues to lumber slowly northwestwards at 6 mph, as it pounds Louisiana, Mississippi, Alabama, and Florida’s Panhandle with torrential rains, high winds, and a damaging storm surge. The eye was partially over water for most of the 15 hours after Isaac’s official landfall at 7:45 pm EDT Tuesday night, but New Orleans radar shows the eye of the storm is now fully ashore near Houma. The radar echoes show some weakening on the west side of the eyewall, where dry air has infiltrated the storm. Wind shear remains light, and upper level outflow over Isaac is as impressive as we’ve seen so far, with a strong outflow channel to the north, and a respectable one to the south, as well. Infrared and visible satellite loops show a very large, symmetric, and well organized storm, and Isaac is going to be able to stay near Category 1 hurricane strength all day today. This will allow Isaac to drop rainfall amounts of 15 – 20″ in some areas of Louisiana before the storm is over. A few rainfall totals from Isaac through 11 am EDT:

9.26″ New Orleans Lakefront Airport
5.59″ Belle Chasse, LA
5.21″ Mobile, AL
3.65″ Hattiesburg, MS
3.42″ Gulfport, MS
2.81″ Biloxi, MS

Figure 1. Morning radar reflectivity image from New Orleans.

A dangerous storm surge event underway
Isaac is bringing a large and dangerous storm surge to the coast from Central Louisiana to the Panhandle of Florida. Late this morning was high tide along much of the coast, and the highest water levels of Isaac are likely being experienced at many locations. At 11:30 am EDT, here were some of the storm surge values being recorded at NOAA tide gauges:

8.0′ Waveland, MS
8.2′ Shell Beach, LA
2.0′ Pensacola, FL
4.6′ Pascagoula, MS
3.4′ Mobile, AL

The peak 11.06′ storm surge at 1:30 am EDT this morning at Shell Beach, which is in Lake Borgne, 20 miles southeast of New Orleans, exceeded the 9.5′ surge recorded there during Category 2 Hurricane Gustav of 2008. In general, the storm surge heights from Isaac have been more characteristic of a strong Category 2 hurricane, rather than the weak Category 1 hurricane one might suppose Isaac is, based on its top sustained winds of 75 – 80 mph. The Saffir-Simpson Scale for ranking hurricanes is only a crude measure of their potential impacts.

A storm surge estimated at 12′ moved up the Mississippi in Plaquemines Parish near Port Sulphur, LA, near 8:30 pm EDT Tuesday, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade New Orleans got after Hurricane Katrina, and were not rated to Category 3 hurricane strength, like the levees protecting New Orleans are. The surge continued upriver, elevating the water levels 10′ in New Orleans (103 miles upstream from the mouth of the Mississippi), 8′ in Baton Rouge (228 miles upstream), and 1.4′ at Knox Landing, an amazing 314 miles upstream. The river was 7′ low due to the great 2012 U.S. drought, and I suspect the near-record low flow rate of the river allowed the storm surge to propagate so far upstream. The salt water from the storm surge will be slow to leave the river, due to the continued winds of Isaac keeping the surge going, plus the very low flow rates of the river. One benefit of the heavy rains of 10 – 20 inches expected to fall over Louisiana over the next two days will be to increase the flow rate of the Mississippi River, helping flush the salt water out of the river. The low flow rates of the Mississippi had allowed salt water to move upriver to just south of New Orleans over the past few weeks, threatening the drinking water supply of Plaquemines Parish.

Figure 2. Tide gauge data from Waveland, Mississippi. The green line shows the storm surge. The red line is the storm tide, the height of the water above Mean Sea Level (MSL.) The storm tide at Waveland currently (9′) is 2′ higher than that of Category 2 Hurricane Gustav of 2008. Image credit: NOAA Tides and Currents.

Tropical Storm Kirk in the Central Atlantic
Tropical Storm Kirk formed Tuesday night in the Central Atlantic. Kirk’s formation at 03 UTC on August 29 puts 2012 in 4th place for earliest formation date of the season’s 11th storm. Only 2005, 1995, and 1933 had an earlier formation date of the season’s 11th storm. Kirk should stay well out to sea and not trouble any land areas.

Figure 3. Morning satellite image of Tropical Storm Kirk.

Invest 98L in the Eastern Atlantic
A tropical wave (Invest 98L) is about 750 miles west-southwest of the Cape Verde Islands, and is moving west to west-northwest at about 15 mph. In their 8 am EDT Tropical Weather Outlook, NHC gave 98L a 50% chance of developing by Friday morning. Several of the models develop 98L into a tropical depression by this weekend, but none of the reliable models foresee that 98L will be a threat to the Lesser Antilles. The storm may be a threat to Bermuda next week, but it is too early to say if it may threaten the U.S.

Jeff Masters

from:    http://www.wunderground.com/blog/JeffMasters/article.html

Jeff Masters On Current Tropical Storms

94L a threat to the Lesser Antilles; Gordon a hurricane; Helene hits Mexico
Posted by: Dr. Jeff Masters, 3:24 PM GMT on August 18, 2012 +22

A large tropical wave that emerged from the coast of Africa Thursday night (Invest 94L) is located a few hundred miles southwest of the Cape Verde Islands off the coast of Africa, and is headed west at 15 – 20 mph. This storm is a threat to develop into a tropical storm that will affect the Lesser Antilles Islands as early as Wednesday. The storm is under moderate wind shear of 10 – 20 knots, and is over waters of 27.5°C. A large area of dry air lies just to the north of 94L, as seen on the latest Saharan Air Layer (SAL) analysis. This morning’s 8:15 am EDT ASCAT pass caught the east side of 94L, and showed a partial surface circulation. Satellite images show just a modest amount of heavy thunderstorm activity, and I expect the earliest that 94L could develop into a tropical depression would be Sunday.

Figure 1. Morning satellite image of Invest 94L.

Forecast for 94L
The latest 8 am EDT run of the SHIPS model predicts that wind shear will be low, 5 – 10 knots, and ocean temperatures will gradually warm from 27.5°C to 28.5°C over the next four days, as 94L tracks westwards towards the Lesser Antilles. As is typical with storms making the crossing from Africa to the Antilles, dry air to the north will likely interfere with development. However, with shear expected to be low, dry air may be less of an issue for 94L than it was for Ernesto or TD 7. The storm should maintain a nearly due west track through Monday night, to a point near 50°W, about 700 miles east of the Lesser Antilles. At that point, a trough of low pressure passing to the north of 94L may be able to pull the storm more to the northwest, as suggested by the latest 06Z (2 am EDT) run of the NOGAPS model, and by three members of the GFS model ensemble forecast (Figure 2.) However, the models have been trending more towards a solution where this trough is not strong enough to influence 94L’s path. This scenario will be more likely if 94L takes its time to develop, since a weaker storm will be smaller and shallower, and less likely to respond to the trough passing to the north. Our two best performing models, the GFS and ECMFW, both take 94L through the Lesser Antilles. The ECMWF, which predicts that 94L will stay weak and not develop, is faster, bringing the storm through the Lesser Antilles on Wednesday. The GFS model is slower, bringing 94L to the Lesser Antilles on Thursday as a hurricane. The models have shown poor run-to-run consistency in both the timing and the track of 94L, so it is difficult to assess which land areas might be most at risk, and when. A database of historical probabilities of storms in the same location as 94L maintained by Dr. Bob Hart of Florida State University reveals that historically, 45% of storms in this location have eventually hit land, with Canada (13% chance) and North Carolina (15% chance) the most likely targets. In their 8 am EDT Tropical Weather Outlook, NHC gave 94L a 40% chance of developing into a tropical depression by Monday morning.

Figure 2. The 00Z (8 pm EDT) run of the GFS model from August 17, 2012, was done 20 different times at low resolution using slightly different initial conditions to generate an ensemble of forecasts (pink lines.) The high-resolution operational GFS forecast is shown in white.

Gordon becomes a hurricane
Hurricane warnings are flying for the central and eastern Azores Islands as Hurricane Gordon heads eastwards at 18 mph. Gordon became the third hurricane of the 2012 Atlantic hurricane season at 5 am Saturday morning, and is sporting an impressive-looking eye on visible satellite loops. Gordon should be able to maintain hurricane status until Sunday, when wind shear will rise steeply to 30 – 40 knots, and ocean temperatures will drop to 25°C. The combined effects of high wind shear, dry air, and cooler waters will likely act to weaken Gordon to a strong tropical storm by the time it arrives in the Azores Islands Sunday night, but the storm will be strong enough to bring damaging winds and heavy rain to the Azores Islands. Gordon is not a threat to any other land areas, and the extratropical remnants of Gordon will not bring any strong winds or significant rain to Europe. The last time the Azores were affected by a tropical storm was in 2009, when Tropical Storm Grace brought 65 mph winds on October 4. No significant damage was reported. Ironically, the last hurricane to affect the Azores was the 2006 version of Hurricane Gordon, which caused minor damage in the Azores, consisting of mostly fallen trees and power outages. However, after Gordon became an extratropical low, four injuries due to falling debris from high wind were reported in Spain, and Gordon brought high winds and rain that affected practice rounds at the Ryder Cup golf tournament in Ireland. About 126,000 homes were without power after the storm in Northern Ireland and one injury was reported.

Figure 3. Morning satellite image of Hurricane Gordon.

Helene makes landfall in Mexico
Tropical Storm Helene made landfall near 10 am EDT as a tropical storm near Tampico, Mexico, with 40 mph winds. Helene’s formation on August 17 ties 2012 with 1933 for the 2nd earliest appearance of the Atlantic’s eighth tropical storm. Helene’s rains should remain south of Texas, but moisture from Helene may feed into a stalled frontal system over the northern Gulf of Mexico and bring heavy rains to the northern Gulf Coast early next week.

from:    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2191