Following Joaquin

Joaquin Close to Category 5 Strength; Rains Inundate Carolinas

By: Bob Henson , 6:01 PM GMT on October 03, 2015

There is plenty of life left in Hurricane Joaquin as it moves away from the Bahamas. An Air Force Hurricane Hunter aircraft detected winds around noon EDT Saturday of 144 knots at the 700-millibar level, with stepped-frequency microwave radiometer (SFMR) data showing estimated surface winds of 138 knots (159 mph). The National Hurricane Center upgraded Joaquin’s strength to top sustained winds of 155 mph in a special advisory at noon EDT Saturday, up from 130 mph in the advisory issued just an hour earlier. This immediately pushed Joaquin from the bottom to the top end of the Category 4 scale. A central pressure of 933 millibars was reported, although a radiosonde deployed in the eye of Joaquin failed, so there is some uncertainty around this estimate. Another Hurricane Hunter aircraft was en route to Joaquin as of early Saturday afternoon. Joaquin’s eye has warmed and cleared over the last few hours, reflecting the rapid restrengthening, although infrared satellite imagery shows that its core of strongest thunderstorms has become smaller and less intense.


Figure 1. Latest satellite image of Hurricane Joaquin.

Joaquin’s burst of strength is especially remarkable given that a strong El Niño is under way (El Niño tends to suppress Atlantic hurricane activity by enhancing wind shear). The last Atlantic storm with sustained winds this strong was Hurricane Igor, in 2010, which peaked at 155 mph. The Atlantic’s last Category 5 was Hurricane Felix, in 2007, with winds topping out at 160 mph. The last El Niño season that managed to produce a Category 5 was 2004, when Ivan formed. However, the El Niño event of 2004-05 was relatively weak, with autumn Niño3.4 anomalies of only around +0.7°C compared to the current value of more than +2.0°C.

Joaquin is also in an area where very few Category 5 track segments have been reported since reliable records began in 1950 (see Figure 2). Record-warm waters in this part of the Northwest Atlantic are likely playing a major role in Joaquin’s unusual strength. Joaquin was designated as a tropical depression on Sunday night, September 27, at latitude 27.5°N. This makes Joaquin one of the strongest Atlantic hurricanes on record to have begun its life as a tropical cyclone at such a high latitude. In fact, Joaquin’s latest location (26.4°N. 70.9°W) is still south of its origin point.

Fortunately for the United States, Joaquin is hustling into the open Atlantic, now moving northeast at 16 mph. Track models are fairly consistent in keeping Joaquin west of Bermuda, but with only a small margin for error. Bermuda is now under a hurricane watch and tropical storm warning; at a minimum, the island can expect high surf, strong winds, and a few squalls from outer-edge rainbands, especially as Joaquin makes its closest approach on Monday.


Figure 2. In this map of all Category 5 hurricanes reported in the Atlantic since 1950, bright purple indicates the segments where Category 5 strength was analyzed. Image credit: The Weather Channel, courtesy Jon Erdman.


Figure 3. Satellite image Hurricane Joaquin taken at noon EDT October 3, 2015. At the time, the hurricane was just below Category 5 strength with top winds of 155 mph. A band of very heavy rain can also been seen feeding into South Carolina, to the northwest of the hurricane. Image credit: NASA/GSFC.


Figure 4. Flooding from heavy rain swamps the intersection of Huger Street and King Street in Charleston, S.C. on Saturday, October 3, 2015. Image credit: Matthew Fortner/The Post And Courier, via AP.

Severe flooding likely in South Carolina Saturday and Sunday
As expected, a band of torrential rain has materialized over South Carolina, paving the way for an especially dangerous situation from Saturday afternoon into Sunday. As of midday Saturday, the heaviest rain extended from the south half of the South Carolina coastline northwest across the state to the hilly Uplands region. The swath of intense rain will pivot very slowly in a counterclockwise direction, gradually translating southward over the higher terrain but moving very little near the coastline. This will put the area around Charleston at particular risk of severe flash flooding from Saturday afternoon into Sunday. CoCoRaHS maps show widespread rain totals of 4” – 8” in the Charleston area from 7:00 am EDT Friday to 7:00 am Saturday.


Figure 5. Predicted 15-hour rainfall totals from the HRRR model for the period from 10:00 am Saturday, October 3, to 1:00 am Sunday, October 4. Image credit: NWS/NCEP.

The Charleston area has a reasonable chance of beating the all-time three-day rainfall records below, possibly in just a 24-hour period!

North Charleston, SC (CHS)
11.95”, 6/9/1973-6/11/1973
11.62”, 6/10/1973-6/12/1973
11.40”, 9/19/1998-9/21/1998
10.64”, 9/4/1987-9/6/1987
10.52”, 9/21/1998-9/23/1998
Records begin in 1938

Downtown Charleston, SC (CXM)
12.39”, 6/9/1973-6/11/1973
11.92”, 6/10/1973-6/12/1973
11.73”, 9/5/1933-9/7/1933
11.72”, 9/4/1933-9/6/1933
11.31”, 9/4/1987-9/6/1987
Records begin in 1870

Forecasters are particularly concerned that high-tide cycles in Charleston may coincide with periods of torrential rain, which could produce extreme flash flooding in the city in short order. The Saturday afternoon high tide of 8.2 feet was the highest to occur since Hurricane Hugo in 1989. The next tides will occur in Charleston at 1:34 am and 2:03 pm on Sunday.

Surrounding states are also experiencing heavy rain and flood threats. Mudslides and landslides are possible in the higher terrain of Georgia, South Carolina, and North Carolina. A strengthening of the onshore flow that has persisted for several days over the mid-Atlantic will again raise the risk of significant tidal flooding from Virginia to New Jersey, especially in the Hampton Roads area of Virginia.


Figure 6. GOES-West infrared satellite image covering the Northeast and Central Pacific, taken at 1545Z (11:45 am EDT) Saturday, October 3, 2015. Image credit: CIMMS/SSEC/University of Wisconsin-Madison.

Tropical Storm Oho may threaten Hawaii
The hyperactive Central Pacific broke its record–again–for the most number of named storms in a single season with the christening of Tropical Storm Oho on Saturday. According to NHC’s Eric Blake, Oho is the eighth tropical storm to form in the Central Pacific this year, doubling the previous record of just four. Oho is now located roughly 500 miles south-southeast of Honolulu. The steering patterns that will drive Oho are ill-defined and still evolving, which complicates the track forecast. The Central Pacific Hurricane Center currently projects Oho to arc northwest over the next couple of days, then move more briskly toward the east and northeast on a path that would keep it a couple hundred miles south of Hawaii’s Big Island early next week. There is plenty of room for this forecast to evolve, though. Oho has the chance to become a powerful hurricane, thanks to the weak upper-level flow as well as record-warm waters that have fueled so many other tropical cyclones in the Central Pacific this year. The SHIPS rapid intensification index gives Oho a good chance of rapidly strengthening from Saturday into Sunday. Oho now has top sustained winds of just 40 mph, but most dynamical and statistical models are making Oho a hurricane by Monday, and several bring it to Category 2 status by Thursday.

Elsewhere in the tropics
An array of other systems peppered the Northern Hemisphere tropics on Saturday. In the Central Atlantic, Invest 90L is looking less robust, with NHC now giving it only a 40% chance of development in the next 2 to 5 days. A late-blooming Cape Verde wave between 30°W and 35°W poses little threat over at least the next several days, and strong wind shear at low latitudes will probably cap any later development.


Figure 7. WU’s latest tracking map for tropical cyclones around the globe.

In the Northeast Pacific, Invest 94E is slowly organizing more than 1000 miles southwest of Baja California. NHC gives 94E a 30% chance of developing into a tropical cyclone by Monday and a 50% chance by Thursday. Closer to Mexico, the remants of Tropical Storm Marty could produce heavy rainfall as they move inland on Sunday into Monday. Some moisture from ex-Marty may get entrained into an upper-level storm taking shape early next week in the Southwest U.S., possibly delivering strong thunderstorms to the Arizona deserts on Monday.

In the Central Pacific, still another system–Tropical Depression 8C, the 13th tropical cyclone to form or pass through the Central Pacific this year–formed on Saturday morning about 1100 miles southwest of Honolulu. Moderate southerly shear should keep 8C from developing beyond minimal tropical-storm strength for at least the next couple of days as it pushes westward.

In the Northwest Pacific, Typhoon Mujigae may strengthen slightly over the next 24 hours before it moves into the coast of extreme southern China, southwest of Hong Kong. To the east, Tropical Storm Choi-Wan will slowly gather steam and may become a minimal typhoon early next week before an expected recurvature just east of Japan by midweek.

We’ll have our next update on Sunday afternoon.

Bob Henson

from:    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3139

Hurricane Joaquin Heads Towards the East Coast

Hurricane Warnings for the Bahamas From Joaquin; Threat to U.S. East Coast Grows

By: Jeff Masters and Bob Henson , 3:38 PM GMT on September 30, 2015

Joaquin is now a hurricane, and Hurricane Warnings are up for the Central Bahama Islands as the slowly intensifying storm moves southwest at 6 mph. An Air Force hurricane hunter aircraft made two penetrations of Joaquin’s center on Wednesday morning, and found top surface winds of 80 mph, a central pressure of 971 mb, and a huge 54-mile diameter eye with a fully closed eyewall. Joaquin continues to battle high wind shear of 20 knots due to strong upper-level winds out of the north-northwest, but this wind shear had fallen by about 5 knots since Tuesday morning. Water vapor satellite loops show that a large area of dry air lay to the northwest of Joaquin, and the strong wind shear was driving this dry air into Joaquin’s core, keeping intensification slow. Visible and infrared satellite loops show that Joaquin has developed a large Central Dense Overcast (CDO) of high cirrus clouds over the center, characteristic of intensifying storms, and the hurricane’s large eye was beginning to be apparent. Upper level winds analyses from the University of Wisconsin show that the hurricane has developed an impressive upper-level outflow channel to the southeast, which is supporting the intensification process. Ocean temperatures in the region are near 30°C (86°F)–the warmest seen there since record keeping began in 1880.


Figure 1. Latest satellite image of Joaquin.

The U.S. outlook for Joaquin
A hurricane watch could be required for portions of the U.S. East Coast as early as Thursday night. The forecast for Joaquin is very complex, and the confidence in both the intensity and track forecast for the storm is low. Joaquin is trapped to the south of a high pressure system whose clockwise flow will push the cyclone very slowly to the southwest or west-southwest at about 3 – 6 mph. As the storm progresses to the southwest, the strong upper-level winds out of the north currently bringing high wind shear of 20 knots will gradually decrease, continuing to allow Joaquin to strengthen. The 8 am EDT Wednesday run of the SHIPS model predicted that wind shear over Joaquin would fall to the moderate range, 10 – 20 knots, on Thursday and Friday. These conditions should allow Joaquin to intensify to a Category 2 hurricane by Thursday. As Joaquin progresses to the west, the storm will also increasingly “feel” the steering influence of a strong upper-level trough of low pressure situated over the Eastern United States on Friday, and begin to turn north. These winds may also open up another upper-level outflow channel to the northwest of Joaquin on Friday, potentially allowing the storm to intensify to Category 3 strength. However, as Joaquin gets closer to this trough, its winds will bring high wind shear of 20+ knots, likely halting the intensification process and causing weakening by Sunday.


Figure 2. Our two top models for forecasting hurricane tracks, both run at 8 pm EDT Tuesday September 29, 2015 (00Z Wednesday) , came up with two very different solutions for the path of Joaquin. The GFS model showed Joaquin making landfall in Virginia, while the European model took the storm to the northeast out to sea without hitting the U.S. Image credit: wundermap with the “Model Data” layer turned on.



Figure 3. The ensemble runs of our two top models for forecasting hurricane tracks, both run at 8 pm EDT Tuesday September 29, 2015 (00Z Wednesday). The 50 members of the European model ensemble (top) and the 20 members of the GFS model ensemble (bottom) both had numerous model runs that took Joaquin into U.S. East Coast, and ones that missed the U.S. coast entirely. Ensemble runs take the operational version of the model and run it at lower resolution with slightly different initial conditions, to generate an “ensemble” of possible forecasts. The operation high-resolution (and presumably best-guess) forecast for the models is shown in red. The European model ensemble had four members that tracked the movement of Joaquin exceptionally well during the previous 12 hours; three of those four members had tracks for Joaquin that missed the U.S., and one that hit the coast near New York City. Image taken from a custom software package used by TWC.

The big trend from the 00Z Wednesday (8 pm EDT Tuesday) suite of computer model guidance was a marked convergence toward a landfall in the vicinity of North Carolina or Virginia. The 00Z HWRF and GFDL models were joined by the 00Z GFS in hooking Joaquin toward the northwest on Friday and accelerating the hurricane into the coast between Cape Hatteras, NC, and the Delmarva Peninsula as a significant hurricane on Saturday/Sunday. The high-resolution HWRF and GFDL output showed central pressures in the 940-950 mb range at landfall, with wind speeds on par with a Category 2 hurricane. The 00Z UKMET solution angled more north-northwestward, with Joaquin arriving near the southern end of the Delmarva and scraping up the coast into eastern New Jersey and New York. Among the major dynamical models, only the European (ECMWF) model remained adamant that Joaquin would head to sea well before reaching the southeast U.S., although its 00Z track was a bit west of previous runs. The leftward hook prominently featured in the other models is being driven by the increasingly negative tilt (NW-to-SE) to the upper trough deepening over the eastern U.S. late this week. The models are projecting that this trough would pull in Joaquin on its northeast side, in much the same way that a strong upper-level low did with Hurricane/Superstorm Sandy in 2012. However, in Joaquin’s case, the process would unfold a couple of hundred miles to the south. The ECMWF run shows a very similar upper-level pattern to the other models, but the timing of the trough’s interaction with Joaquin and with Invest 90L is such that the hurricane is shunted to sea instead of being tucked into the northeast side of the trough. 90L was centered at 8 am EDT Wednesday about 1000 miles east-northeast of Joaquin. In their 8 am EDT Wednesday Tropical Weather Outlook, NHC gave 90L 2-day and 5-day odds of development of 40% and 70%, respectively.


Figure 4. Model track guidance initialized at 12Z Wednesday (8 am EDT) shows a continued clustering of model solutions toward North Carolina and the mid-Atlantic. This early-track guidance uses 12Z data on Joaquin to update the previous model runs from 06Z. This map does not include the ECMWF model, whose 00Z operational run took Joaquin out to sea. Image credit: Levi Cowan, tropicaltidbits.com.

Back in 2012, the ECMWF model caught on to the leftward hook of Sandy’s track several days before other models. The ECMWF’s high overall skill means we cannot entirely discount its out-to-sea forecast for Joaquin just yet. At the same time, the strong consistency among other leading models in projecting a NC/mid-Atlantic landfall cannot be ignored. We can gain more perspective on this scenario by looking at the ECMWF and GFS ensemble output from 00Z Wednesday. In each ensemble, the model is run a number of times for the same situation, but with the starting conditions varied slightly to represent the uncertainty in our starting-point observations of the atmosphere. The ECMWF and GFS ensembles from 00Z Wednesday are much more similar in flavor than you might expect from looking at their single operational runs. Both models have a majority of ensemble members heading for North Carolina and the mid-Atlantic, with a few outliers heading to sea.

If Wednesday’s 12Z (8 am EDT) models continue to zero in on a NC/VA landfall, and especially if the ECMWF comes more fully around, then this solution will become a more high-confidence forecast. The NHC has been nudging its “cone of uncertainty” toward the left, still splitting the difference between the ECMWF and other solutions while acknowledging the westward trend. The entire U.S. coast from the Outer Banks of NC to southern New England was located in the 5-day cone issued at 11 am EDT Wednesday and valid at 2 am EDT Monday. Even if NHC moves more fully toward the NC/mid-Atlantic scenario, we can still expect to see a large swath of coastline remaining in the “cone” as we get closer to Joaquin’s eventual landfall.

Potential impacts from Joaquin
Apart from the remaining uncertainty about a U.S. landfall, Joaquin is now poised to bring hurricane-force conditions into or very close to the southeastern Bahamas. WIth luck, these islands will remain on the weaker left-hand side of Joaquin. If the hurricane makes a sharp turn to the north on Friday as predicted, the effects should be considerably less on the northwestern Bahamas.

It is relatively rare for a hurricane to make a Sandy-like left hook into the U.S. East Coast. Such a track was unprecedented for New Jersey in hurricane annals, and even in the NC/VA area, it is uncommon enough that the likely effects would be both unusual and high-impact. The closest analogue from recent years is 2003’s Hurricane Isabel. After a much longer life as a Cape Verde system and a Category 4 hurricane from the Central Atlantic (briefly a Category 5), Isabel angled sharply northwestward and made landfall on North Carolina’s Outer Banks as a strong Category 2 hurricane. Isabel then continued on a fairly direct track to western Pennsylvania as it weakened. Isabel’s trajectory brought huge surf to the coast from North Carolina to New Jersey, with a major storm surge pushing into the Chesapeake Bay and nearby waterways, plus widespread impacts from high wind and heavy rain. Joaquin is not as large or long-lived a storm as Isabel, but if it moved slightly to the north of Isabel’s path, its track could be even more favorable for a Chesapeake surge. Hurricane-force winds would be another factor to contend with, especially just north of Joaquin’s track during and just after landfall. Storm surge expert Dr. Hal Needham of LSU has a detailed look at the potential for storm surge from Joaquin along the U.S. East Coast in his Wednesday morning blog post, Widespread Storm Surge Event to Impact U.S. Atlantic Coast.

One very worrisome aspect of Joaquin is the torrential rains that it could bring from the Carolinas to the Northeast and perhaps even New England. Heavy rains and scattered flash flooding have already occurred in parts of these areas over the last 24 hours, as a preexisting front is overtopped by near-record amounts of water vapor streaming over the region ahead of the trough that will help steer Joaquin. The hurricane itself, arriving after several days of antecedent rainfall, has the potential to produce truly historic rainfall totals. This morning’s 7-day outlook from the NOAA Weather Prediction Center, which goes with the NC/mid-Atlantic scenario, shows widespread 5-10″ amounts from North Carolina to southern New England. Model output suggests that localized 7-day totals of 10-20″ or more are not out of the question, depending on Joaquin’s exact track. We’ll have more on the ongoing and potential flood risk in our afternoon post.


Figure 5. Projected 7-day rainfall amounts from 12Z Wednesday, September 30, to 12Z October 7. Image credit: NOAA Weather Prediction Center.

We’ll have a new post this afternoon.

Jeff Masters and Bob Henson

from:    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3131