La Nina Tagged ‘La Nina’

Quiet Hurricane Season Expected

Saturday, April 7th, 2012

fr/Dr. Jeff Masters:

CSU: expect a quiet 2012 Atlantic hurricane season; EF-3 tornado confirmed in Texas
Posted by: JeffMasters, 2:47 PM GMT on April 05, 2012 +29
Expect one of the quietest Atlantic hurricane seasons since 1995 this year, say the hurricane forecasting team of Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) in their latest seasonal forecast issued April 4. They call for an Atlantic hurricane season with below-average activity: 10 named storms, 4 hurricanes, and 2 intense hurricanes. An average season has 10 – 11 named storms, 6 hurricanes, and 2 intense hurricanes. The 2012 forecast calls for a below-average chance of a major hurricane hitting the U.S., both along the East Coast (24% chance, 31% chance is average) and the Gulf Coast (24% chance, 30% chance is average). The Caribbean is forecast to have a 34% chance of seeing at least one major hurricane (42% is average.) Four years with similar pre-season March atmospheric and oceanic conditions were selected as “analogue” years that the 2012 hurricane season may resemble: 200920011965, and 1957. These years all had neutral to El Niño conditions during hurricane season. The average activity for these years was 9.5 named storms, 4.8 hurricanes, and 2.3 major hurricanes.


Figure 1. Departure of sea surface temperature (SST) from average for April 5, 2012, as computed by NOAA’s NESDISbranch. SSTs in the hurricane Main Development Region (red box) were near average to below-average.

Why the forecast of a quiet season?
The CSU team cited two main reasons why this may be a quieter than average hurricane season:

1) La Niña has weakened rapidly over the tropical Eastern Pacific over the past month, and is expected to be gone by the end of April. In its wake, El Niño conditions may develop in time for the August – September – October peak of hurricane season. If El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart. The CSU team is leaning towards putting their trust in the ECMWF model, which is predicting that a weak El Niño event will be in place by fall.

2) Sea surface temperatures (SSTs) in the Main Development Region (MDR) for hurricanes from the Caribbean to the coast of Africa between 10°N and 20°N were near average to below average in March 2012. Virtually all African waves originate in the MDR, and these African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely. This year’s SSTs in the MDR are among the coolest we’ve seen since our current active hurricane period began in 1995. The cool temperatures are largely due to strong surface winds that blew during the winter over the tropical Atlantic in response to the positive phase of the North Atlantic Oscillation (NAO.) The strong winds stirred up the water, bringing up cooler waters from the depths.

How good are the April forecasts?
The forecasters are using a new statistical model developed last year for making April forecasts, so we don’t have a long enough track record to judge how good the new model is. The new model correctly predicted a more active than average season for last year, though called for more activity than was actually observed. However, April forecasts of hurricane season activity are low-skill, since they must deal with the so-called “predictability barrier.” April is the time of year when the El Niño/La Niña phenomenon commonly undergoes a rapid change from one state to another, making it difficult to predict whether we will have El Niño, La Niña, or neutral conditions in place for the coming hurricane season. Correctly predicting this is key, since if El Niño, conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart.

CSU maintains an Excel spreadsheet of their forecast errors ( expressed as a mathematical correlation coefficient, where positive means a skilled forecast, and negative means they did worse than climatology) for their their April forecasts. For now, these April forecasts should simply be viewed as an interesting research effort that has the potential to make skillful forecasts. The next CSU forecast, due by June 1, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years.

to read more, go to:    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2067

This Weird Winter Weather

Wednesday, March 7th, 2012

Why Much of North America Skipped Winter

Wynne Parry, LiveScience Senior Writer
Date: 06 March 2012 Time: 05:14 PM ET
Cherry blossoms on March 4, a sign of early spring in Brooklyn.
Cherry blossoms on March 4, a sign of early spring in Brooklyn.
CREDIT: Wynne Parry

For parts of North America, this winter was the winter that nearly wasn’t.

January ranked as the fourth-warmest for the 48 U.S. states on record since 1895. December, too, was above average, although not as significantly. The final analysis for February is not yet in, but weather watchers expect last month to rank above average temperature-wise as well.

Of course, this year hasn’t brought early beach weather for everyone; just ask residents of Alaska and Europe, where a frigid cold snap is blamed for hundreds of deaths. And the warmth has been blamed for contributing to the slew of devastating tornadoes that hit the Midwest and southern U.S. on Friday (March 2).

While scientists have said that global warming willcause an uptick in extreme weather, they are hesitant to link any one event or even an unusual season to climate change. Even so, they say, global warming may play a role in the weird winter weather.

The jet stream

The key to understanding the unusually warm winter lies in the jet stream. It is made up of high-altitude, westerly winds. Its polar branch, the one important for determining winter weather, travels over the mid-latitudes of the Northern Hemisphere in winter, according to Jeff Masters, director of meteorology at the weather service and news site Weather Underground.

The polar jet stream divides cold Arctic air to the north from warmer air to the south. This year, meteorologists say, the jet stream has kept the cold air bottled up farther north than usual.

As a result, warmer-than-usual temperatures this year have graced much of the United States, particularly in New England, the Great Lakes and the Upper Plains, according to Mark Paquette, a meteorologist with AccuWeather.com. Southern Canada, too, has gotten its share of mild winter weather

The polar jet stream is influenced by natural patterns, the most prominent being fluctuations in the Northern Annular Mode, also called the Arctic Oscillation. When the mode is in its so-called positive phase, air pressure over the far north remains low, leading to a stronger jet stream. This keeps the cold Arctic air bottled up to the north. The negative phase, meanwhile, is associated with a weaker, meandering jet that allows cold air to spill south.

Reversals

Until late January, the mode was in its positive phase, resulting in warmer temperatures farther north.

But a reversal of phase allowed the jet stream to meander some, and let Arctic cold air move down into Eastern Europe. The result was a cold snap that is blamed for killing hundreds.

The mode has shifted again since then. In fact, a strong jet stream contributed to the tornados that hit the south and the Midwest last week, as did the arrival of warm, moist air from the Gulf of Mexico, according to Masters, who discusses the tornados on his blog.

La Niña and the future

Another large-scale atmospheric pattern, one related to temperatures in the equatorial Pacific Ocean, is also at play. This winter La Niña, associated with cooler water temperatures in the Pacific, has been in effect. La Niña is typically associated with drier-than-normal conditions for the southern and eastern U.S. — largely consistent with precipitation this winter, according to Deke Arndt, chief of the climate monitoring branch at the National Climatic Data Center (NCDC) in Boulder, Colo.

“The dryness looks like what we would expect with La Niña, the warmth we saw is consistent with the positive Arctic Oscillation,” Arndt said. “The two of them tougher, all else being equal, would tend to produce a warmer and drier winter, especially east of the Rockies.”

Paquette predicts an end to this trend. “Mother Nature or weather patterns have a way of evening themselves out. I think it only matter of time before this mild dry pattern flips and we get into a much different weather pattern.”

from:    http://www.livescience.com/18877-mild-winter-weather.html

Hurricane Season Update

Sunday, September 18th, 2011

Hurricane Season Hits Pause, But Isn’t Over

by Brett Israel
Date: 16 September 2011 Time: 04:05 PM ET
hurricane maria hits newfoundland

 

Hurricane Maria heads toward Newfoundland today, but there are no storms behind it….for now.
CREDIT: NOAA/NASA GOES-13 satellite.

Mid-August marked an uptick in the number of tropical storms and hurricanes forming in the Atlantic Ocean, with one storm always seeming to follow on the heels of another. But lately, the tropics have quieted down.

Hurricane Maria, the third hurricane of the 2011 season, is expected to hit Newfoundland, Canada, today (Sept. 16), but there are no other tropical cyclones (hurricanes and tropical storms) after this one the radar. But don’t think for a second that hurricane season is headed for an early exit, experts say.

“In no way, shape or form is this season over,” said Dennis Feltgen of the National Hurricane Center in Miami.

If, for some odd reason, no other tropical storms were to form this year, it would be the earliest end ever for an Atlantic hurricane season. The earliest date in the satellite era of the last active tropical cyclone in a given year was Sept. 21, 1993. Hurricane season officially ends Nov.1.

Feltgen and others say we’re not likely to set a new record this year.

“I would be incredibly surprised if Maria was the last tropical cyclone in the Atlantic,” said Phil Klotzbach, an atmospheric scientist at Colorado State University in Fort Collins. “While it looks like we’re going into a somewhat quieter period for a little bit, it’s not that unusual to have a quiet period during an active season,” Klotzbach said.

This season was predicted to be a doozy, with 14 to 19 named storms (which include tropical storms and hurricanes), seven to 10 hurricanes and three to five major hurricanes (Category 3 or higher). So far there have been 14 named storms (Nate formed shortly after Maria, but dissipated after striking Mexico shortly after it developed), three hurricanes and two major hurricanes (Irene and Katia).

The tropics seem to have quieted down as storms shift their birthplace to the west in the Atlantic basin. At the beginning of the season, tropical cyclones form near Cape Verde, off the coast of Western Africa. Toward the end of the season, they begin closer to the West Caribbean. This puts the southeastern United Sates in the crosshairs. October is typically an active month for that region.

Most of the global models suggest that another storm should develop in about nine days, Klotzbach said. And with the warm Atlantic waters and La Niña’s return — which has been linked to active hurricane seasons — more big storms could be on the way.

from:   http://www.livescience.com/16104-hurricane-season-lull.html

“It’s nice we got a little chance to breathe and collect our thoughts, but we are far from over,” Feltgen said.

Heat & Hurricanes & Rain & Flooding

Friday, September 9th, 2011
Hottest U.S. summer in 75 years; La Niña is back; Nate and Maria update
Posted by: JeffMasters, 2:32 PM GMT on September 09, 2011 +3
The U.S. had its hottest summer in 75 years, and Texas smashed the record for hottest summer ever experienced by a U.S. state since record keeping began in 1895, NOAA’s National Climatic Data Center said yesterday. The June – August average temperatures in Texas and Oklahoma were a remarkable 1.6°F and 1.3°F warmer than the previous hottest summer for a U.S. state, the summer of 1934 in Oklahoma. Texas’ summer was 2.5°F hotter than their previous hottest summer, in 1998. Louisiana had its hottest summer on record in 2011, and the 4th hottest summer for any U.S. state since record keeping began in 1895. For the U.S. as a whole, the summer of 2011 was the 2nd warmest summer on record, just 0.1°F behind the notorious Dust Bowl summer of 1936. Fifteen states had a summer average temperature ranking among their ten warmest. Washington and Oregon were the only states across the lower 48 to have below-average summer temperatures. Texas also had its driest summer on record, with rainfall 5.29 inches (134.4 mm) below the long-term average, and 1.04 inches (26.4 mm) less than the previous driest summer in 1956. New Mexico had its second driest summer, Oklahoma its third driest summer, and New Jersey and California had their wettest summers on record. The U.S.Climate Extremes Index (CEI), which is sensitive to climate extremes in temperature, rainfall, dry streaks, and drought, indicated that an area nearly four times the average value was affected by extreme climate conditions during summer 2011. This is the third largest summer value of record, and came on the heels a spring season that was the most extreme on record. The CEI goes back to 1910.
Figure 1. Average temperatures for the summer in Texas and Oklahoma, at 86.8 degrees F (30.4 degrees C) and 86.5 degrees F (30.3 degrees C), respectively, exceeded the previous seasonal statewide average temperature record for any state during any season. The previous warmest summer statewide average temperature was in Oklahoma, during 1934, at 85.2 degrees F (29.6 degrees C). Image credit: National Climatic Data Center.

More bad news for Texas: La Niña is back
La Niña, which contributed to extreme weather around the globe during the first half of 2011, has re-emerged in the tropical Pacific Ocean and is forecast to gradually strengthen and continue into winter, NOAA announced yesterday. Over the past two weeks, ocean temperatures have cooled significantly in the Equatorial Pacific off the coast of South America. Ocean temperatures in the region 120°W – 170°W and 5°S – 5°N, called the Niño 3.4 region, were 0.6°C cooler than average over the first week of September. The threshold for a weak La Niña is temperatures 0.5° cooler than average, so we are now experiencing weak La Niña conditions. Drought conditions are common over the southern tier of states during a La Niña event, since the cooling of the equatorial Pacific waters usually pushes the jet stream such that rain-bearing low pressure systems pass through the Midwest and avoid the South. It is likely that the drought gripping Texas, Oklahoma, and New Mexico will continue well into 2012, due to the emergence of La Niña. La Niña events also typically cause wetter than normal winters in the Pacific Northwest and Ohio Valley, colder winters in the Pacific Northwest and northern Plains, and warmer temperatures in the southern states.


Figure 2. Departure of Sea Surface Temperature (SST) from average on September 8, 2011. Cooler than average waters in the equatorial East Pacific signify the emergence of La Niña. In the Atlantic, SSTs remain very warm in the Main Development Region between the coast of Africa and Central America, including the Caribbean. The Gulf of Mexico is cool where Tropical Storm Lee stirred up the water, and the waters off the Mid-Atlantic and New England coasts are cool due to the passage of Hurricane Irene. Image credit: NOAA/NESDIS.

Tropical Storm Nate
Tropical Storm Nate continues to remain nearly stationary in Mexico’s Bay of Campeche. Latest visible satellite loops show that Nate is having trouble with the dry air to its north, which is getting wrapped into the circulation and interfering with intensification. Since the storm is stationary, it is upwelling cooler waters from the depths that are also slowing intensification. Wind shear has fallen to the low range, near 5 knots, so once Nate manages to wall off the dry air to its north and begin moving away from the pool of cool water beneath it, steady intensification should occur. Nate probably has time to intensify to a strong Category 1 hurricane, and perhaps a Category 2 hurricane, before making landfall Sunday in Mexico. The main hazard to Mexico will probably be very heavy rains that will cause flash flooding and mudslides. Thanks to last night’s dropsonde mission by the NOAA jet, the computer models have now come into much better agreement on the future path of Nate. A ridge of high pressure is expected to build in to the north of the storm, forcing it westward or southwestward to a landfall in Mexico. Nate is too far south to be turned northwards towards Louisiana, as some model runs were suggesting yesterday.

Nate is a small storm, and is not likely to bring significant rains to Texas; only extreme South Texas near Brownsville could see an inch or so of rain over the weekend from an outer spiral band of Nate. Our latest wundermap wind forecast map from the European Center model, with the fire layer turned on, shows that Nate’s wind field on Saturday and Sunday will not be large enough to fan the fires burning in Texas.


Figure 3. True-color MODIS image of Tropical Storm Nate taken at 1:40 pm EDT Thursday September 8, 2011. At the time, Nate was a tropical storm with 60 mph winds. Image credit: NASA.

Tropical Storm Maria
Tropical Storm Maria is not changing much in intensity it bears down on the Lesser Antilles Islands, data from an An Air Force Reserve hurricane hunter aircraft currently investigating the storm reveal. Top winds found by the aircraft at their flight level of 5,000 feet were just 48 mph as of 10am EDT, though some stronger surface winds were observed by their SFMR surface wind instrument. Satellite loops show that Maria’s heavy thunderstorms have steadily increased in areal coverage and intensity this morning. Maria has grown into a very large tropical storm, and will bring heavy rains and strong gusty winds to nearly all of the islands in the Lesser Antilles. There is still a moderate 10 – 15 knots of wind shear affecting Maria, and this is slowing down intensification. Maria passed just south of buoy 41101 this morning. Sustained winds at the buoy ranged from 22 – 37 mph this morning, and the pressure dropped to 1003 mb. Martinique radar shows heavy rains from Maria are now affecting the islands, but the thunderstorms are not well-organized into spiral bands.

The intensity forecast models predicts steady strengthening for Maria, and I think likely that Maria will be a tropical storm with 50 – 60 mph winds in the Virgin Islands and Puerto Rico on Saturday, and develop into a Category 1 hurricane shortly after pulling away from Puerto Rico on Saturday night or Sunday morning. The northeastern portion of the Dominican Republic with get heavy rains from Maria, but not tropical storm-force winds. The computer models are unified on taking Maria across the Northern Lesser Antilles, Virgin Islands, and close to eastern Puerto Rico, but then diverge on how strong the steering influence a trough of low pressure forecast to move off the U.S. East Coast early next week will have. The majority of the models predict that the Turks and Caicos Islands and the Bahamas will miss seeing the core of Maria, and the storm will curve to the northwest and then north between the U.S. East Coast and Bermuda on a track that would likely take Maria near Newfoundland, Canada. However, two models–the very reliable ECMWF, and the less reliable NOGAPS–predict that Maria will not get picked up by the trough, and instead will plow straight through the Turks and Caicos Islands and Bahamas towards Florida. Given that the ECMWF model predicts an unrealistically weak storm and the NOGAPS model was our poorest-performing major model last year, I believe a more northerly path missing the Turks and Caicos Islands and Bahamas is more likely. We need a dropsonde mission by the NOAA jet to help reduce some of the track uncertainty, but unfortunately we have only one such airplane, and it is tied up flying missions for Tropical Storm Nate in the Gulf of Mexico.

Lee’s rains trigger historic flooding in New York and Pennsylvania
Rivers in New York and Pennsylvania swollen by record rains from the remains of Tropical Storm Lee have mostly crested and are on their way down this morning, but it will likely be another day before many of the 120,000 people evacuated from the historic floods can return to their homes. Flooding in many areas of Pennsylvania and New York exceeded that ofHurricane Agnes of 1972, which did $11.8 billion in damage (2010 dollars), and was the costliest hurricane in Pennsylvania’s history. Binghamton, New York received 8.48″ of rain in the 24 hours ending at 8 am EDT yesterday. This is nearly double the previous all-time record set just last year, when 4.68″ fell on Sep 30 – Oct. 1, 2010. Binghamton has also already broken its record for rainiest year in its history; records go back to 1890. The Susquehanna River at Binghamton crested at 25.71′, its highest level since records began in 1847, and spilled over the flood walls protecting the city. Rainfall amounts in Pennsylvania were even greater, with Harrisburg receiving 13.30″, and a storm-maximum 15.37″ falling in Elizabethtown, Pennsylvania. In Wilkes-Barre, PA, the Susquehanna River crested at 38.83′ at 1:45 am this morning, just below the 41′ flood wall protecting the city. The flood walls were 37′ back in 1972 when Hurricane Agnes’ rains pushed the Susquehanna River to 41′, flooding the downtown area with 9′ of water, damaging or destroying 25,000 buildings and causing $1 billion in damage.

 

to read more and see the comments, go to:    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1923