Hurricane Hunters find tropical storm winds in TD 9
The Air Force Hurricane Hunters are in Tropical Depression Nine, and have discovered a region of 40 - 45 mph winds at the surface, using their SFMR instrument. Flight level winds at their 1000 foot altitude spiked as high as 49 mph. The surface pressure was 1005 mb, a typical one for a weak tropical storm. Based on these measurements, it is highly likely that NHC will name this Tropical Storm Isaac at 5 pm EDT. A large area of dry air lies just to the north of the storm, as seen on water vapor satellite loops, and this dry air is interfering with development, allowing only a few clumps of heavy thunderstorms to fire up near TD 9's center, as seen on visible satellite loops. These loops also show some arc-shaped low clouds expanding away from the heavy thunderstorm area on the south side of the center, showing that TD 9 is ingesting dry air that is creating strong thunderstorm downdrafts, robbing the storm of moisture and energy. An analysis of upper level winds from the University of Wisconsin CIMSS shows that an upper level outflow channel has opened to the southwest, and another channel is attempting to open up to the north. A large clump of heavy thunderstorms several hundred miles to the southeast of TD 9 continues to compete for moisture, and is interfering with the low level inflow and upper level outflow of the storm. The center of TD 9 will pass about 50 miles to the north of buoy 41101 near midnight tonight. The next hurricane hunter mission into TD 9 is scheduled for 2 am Wednesday, and there will be a new mission launched every six hours. The NOAA jet is first scheduled to fly into the storm on Thursday afternoon, to do a large-scale dropsonde mission to aid model forecasts.
Figure 1. Satellite image of TD 9 and 96L taken at 10:45 am EDT August 21, 2012. The two storms are connected by a thin line of low clouds. Image credit: NOAA Environmental Visualization Lab.
Intensity forecast for TD 9
The latest 2 pm EDT run of the SHIPS model predicts that wind shear will be low to moderate, 5 - 15 knots, for the next five days. Ocean temperatures will warm from 28°C today to 29°C by Wednesday afternoon, and the total heat content of the ocean will increase sharply during that period. The low wind shear and warm waters will favor strengthening. The main impediment to development through Wednesday will be dry air to the north, though the storm will also have trouble separating from the clump of thunderstorms to its southeast. I expect that TD 9 will continue to struggle with dry air through Wednesday. The official NHC forecast is of a 60 mph tropical storm moving through the Lesser Antilles on Wednesday evening; I put the most likely range of strengths for TD 9 Wednesday evening at 50 - 60 mph. Once TD 9 enters the Eastern Caribbean, wind shear will be low, oceanic heat content high, and the storm should have had enough time to moisten the atmosphere to allow steady strengthening to a hurricane. Intensity forecasts 4 - 5 days out are low in skill, though, and it would not be a surprise at all to see TD 9 struggle like so many other storms have over the past two years, and remain a tropical storm over the next five days. Conversely, rapid intensification into a Category 2 hurricane five days from now, as the official NHC is suggesting may happen, would also not be a surprise.
Figure 2. Daily Oceanic Heat Content or Tropical Cyclone Heat Potential (TCHP) for TD 9. The forecast points are from the 11 am EDT NHC advisory, and the 24 hour forecast point shown here is for 8 pm EDT Wednesday. For tropical cyclones in favorable environmental conditions for intensification (i.e., vertical wind shear less than 15 kt, mid-level relative humidity >50 %, and warm SSTs [i.e., >28.5C]) and with intensities less than 80kt, values of ocean heat content greater than 50 kJ/cm^2 (yellow and warmer colors) have been shown to promote greater rates of intensity change. TD 9 will be crossing into such a region early Wednesday morning, and will enter a region of very high TCHP south of Hispaniola on Friday morning (the 72 hour forecast point.) Image credit: NOAA/RAMMB.
Latest model runs for TD 9
The latest set of 12Z (8 am EDT) model runs for TD 9 are fairly unified for the coming three days, showing a west to west-northwest track to a point just south of Hispaniola. Most of the models then predict a more west-northwest track across Southwest Haiti and into eastern Cuba, as TD 9 responds to a small trough of low pressure over the Southeast U.S. A notable exception is our best-performing model, the ECMWF, which keeps TD 9 south of Hispaniola, and takes the storm more to the west over Jamaica by Saturday, and then into the Yucatan Channel between Mexico and Cuba by next Tuesday. We'll have to wait another day to see where the center of TD 9 consolidates before judging which model solution is likely to be correct; reformations of the center closer to bursts of heavy thunderstorm often cause the center point to shift around in the early stages of development, leading to large changes in the forecast track many days later. TD 9 is a threat to affect Tampa during the Republican National Convention, August 27 - 30. I blogged about the climatological chances of a hurricane causing an evacuation of Tampa during the convention in a post last week, putting the odds at 0.2%. The odds in the current situation are higher, probably near 2%. It would take a "perfect storm" sort of conditions to all fall in place to bring TD 9 to the doorstep of Tampa as a hurricane during the convention, but that is one of the possibilities the models have been suggesting could happen.
Disturbance 96L off the coast of Africa
A large tropical wave in the eastern Atlantic about 550 miles southwest of the Cape Verde Islands (Invest 96L) is headed west at 15 mph. This disturbance has an impressive amount of spin, as seen on visible satellite loops, and a respectable amount of heavy thunderstorm activity that is increasing. The storm is under a light 5 - 10 knots of wind shear. Given that TD 9 has moistened up the atmosphere ahead of 96L, this disturbance should have less of a problem with dry air. In their 2 pm EDT Tropical Weather Outlook, NHC gave 96L a 60% chance of developing into a tropical cyclone by Thursday afternoon. This disturbance will track nearly due west the next three days, then is expected to turn more to the west-northwest late this week, bringing it close to the northern Lesser Antilles Islands by Sunday.
Disturbance 95L in the Gulf of Mexico near the Texas/Mexico border
A region of disturbed weather (Invest 95L) is in the Gulf of Mexico, just northeast of Tampico, Mexico. In their 2 pm EDT Tropical Weather Outlook, NHC downgraded the chances of 95L developing to 20%. The Air Force hurricane hunter aircraft scheduled to investigate 95L this afternoon was cancelled. Radar out of Altamira, Mexico does not show any organization to the precipitation echoes and visible satellite loops show that 95L is small and disorganized. The computer models show that 95L should drift westwards, and may move over Mexico on Wednesday.
I'll have a new post in the morning.
Jeff Masters
Reader Comments
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Latest center pressure?
F TD 10 JK LOL
D 90%
Super strong ridge and a wnw movement
Georges had a strong ridge north and a wnw movement
San FELIPE 200mph in Caguas
Approaching the center now.
Funny a hurricane hunter aircract flying 1000 feet above the ocean in the storm does not agree with you.
good to know thanks.
Suddenly, Isaac!
He always states that every storm is going west and straight for the caymans.
He is the Jason of the cayman islands....
Thank you!
I think this is a very well put together "unofficial" track that takes into consideration the long-term uncertainties.
Sorry, I would prefer you try to seek your rain from elsewhere. We don't want a hurricane to come knocking on our doorstep thank you very much.
all the local websites and baynews9, our 24 hours news has been reporting this, since it came off Africa, since the RNC is in Tampa. I might venture out tonight to pick up some water since its on sale at winn dixie I think for a great price, just incase.
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
2100 UTC TUE AUG 21 2012
CHANGES IN WATCHES AND WARNINGS WITH THIS ADVISORY...
NONE.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* MARTINIQUE
* DOMINICA
* GUADELOUPE AND THE SURROUNDING ISLANDS...AND ST. MARTIN
* ST. KITTS...NEVIS...ANTIGUA...MONTSERRAT...ANGUILLA... AND BARBUDA
* SABA...ST. EUSTATIUS...AND ST. MAARTEN
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* BRITISH VIRGIN ISLANDS
* PUERTO RICO...VIEQUES...CULEBRA...AND THE U.S. VIRGIN ISLANDS
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.
A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.
INTERESTS ELSEWHERE IN HISPANIOLA AND CUBA SHOULD MONITOR THE
PROGRESS OF ISAAC.
TROPICAL STORM CENTER LOCATED NEAR 15.4N 53.9W AT 21/2100Z
POSITION ACCURATE WITHIN 20 NM
PRESENT MOVEMENT TOWARD THE WEST OR 275 DEGREES AT 15 KT
ESTIMATED MINIMUM CENTRAL PRESSURE 1006 MB
MAX SUSTAINED WINDS 35 KT WITH GUSTS TO 45 KT.
34 KT....... 40NE 0SE 0SW 0NW.
12 FT SEAS.. 40NE 0SE 0SW 0NW.
WINDS AND SEAS VARY GREATLY IN EACH QUADRANT. RADII IN NAUTICAL
MILES ARE THE LARGEST RADII EXPECTED ANYWHERE IN THAT QUADRANT.
REPEAT...CENTER LOCATED NEAR 15.4N 53.9W AT 21/2100Z
AT 21/1800Z CENTER WAS LOCATED NEAR 15.3N 53.2W
FORECAST VALID 22/0600Z 15.6N 56.4W
MAX WIND 40 KT...GUSTS 50 KT.
34 KT... 50NE 30SE 20SW 50NW.
FORECAST VALID 22/1800Z 15.9N 59.8W
MAX WIND 45 KT...GUSTS 55 KT.
34 KT... 60NE 30SE 30SW 60NW.
FORECAST VALID 23/0600Z 16.3N 63.1W
MAX WIND 50 KT...GUSTS 60 KT.
50 KT... 20NE 0SE 0SW 20NW.
34 KT... 70NE 40SE 30SW 70NW.
FORECAST VALID 23/1800Z 16.6N 66.3W
MAX WIND 65 KT...GUSTS 80 KT.
50 KT... 40NE 30SE 20SW 40NW.
34 KT... 90NE 60SE 40SW 90NW.
FORECAST VALID 24/1800Z 17.0N 71.0W
MAX WIND 75 KT...GUSTS 90 KT.
50 KT... 50NE 30SE 20SW 50NW.
34 KT...110NE 70SE 50SW 110NW.
EXTENDED OUTLOOK. NOTE...ERRORS FOR TRACK HAVE AVERAGED NEAR 175 NM
ON DAY 4 AND 225 NM ON DAY 5...AND FOR INTENSITY NEAR 20 KT EACH DAY
OUTLOOK VALID 25/1800Z 19.5N 75.0W
MAX WIND 75 KT...GUSTS 90 KT.
OUTLOOK VALID 26/1800Z 21.5N 78.0W...INLAND
MAX WIND 65 KT...GUSTS 80 KT.
REQUEST FOR 3 HOURLY SHIP REPORTS WITHIN 300 MILES OF 15.4N 53.9W
NEXT ADVISORY AT 22/0300Z
$$
FORECASTER BEVEN
NNNN
here we go with them, they are going to have a ball covering this.
Oh there is a logical reason in PR - they are facing a TS or Hurr and everyone wants to gas up - still makes it gouging which IMHO is tantamount to legalised pre-strike looting - however, back to TD 09
5:00 PM AST Tue Aug 21
Location: 15.4°N 53.9°W
Moving: W at 17 mph
Min pressure: 1006 mb
Max sustained: 40 mph
WE HAVE ISAAC
Great to be safe than sorry and all... but keep in mind any impacts to the US will be a week away. A lot can and will change between now and then. I would start worrying if I were in the cone 3-4 days out. Way too early, but if I were in the islands I would be stocking up on supplies.
It official we have TS Issac:
...AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT FINDS THAT THE DEPRESSION HAS BECOME A TROPICAL STORM...
5:00 PM AST Tue Aug 21
Location: 15.4°N 53.9°W
Moving: W at 17 mph
Min pressure: 1006 mb
Max sustained: 40 mp
THE I NAME AGAIN
Let me see if I got this right......The EURO is showing exactly what he is saying and that's pulling something out his @ss?? Get a grip......
For those curious about the euro ensemble data this is a cool link.
Go play around and get the N America loop playing...
Look at the shaded areas; Those are the std deviations of the different members that comprise the ens mean.
This run shows that an eastward bias from the ops run will be statistically more likely, based on the ensemble members' runs.
Questions? Comments?
TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 45 MILES...75 KM
TO THE NORTHEAST OF THE CENTER.
WTNT34 KNHC 212050
TCPAT4
BULLETIN
TROPICAL STORM ISAAC ADVISORY NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
500 PM AST TUE AUG 21 2012
...AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT FINDS THAT THE
DEPRESSION HAS BECOME A TROPICAL STORM...
SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...15.4N 53.9W
ABOUT 500 MI...810 KM E OF GUADELOUPE
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...W OR 275 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1006 MB...29.71 INCHES
WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...
NONE.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* MARTINIQUE
* DOMINICA
* GUADELOUPE AND THE SURROUNDING ISLANDS...AND ST. MARTIN
* ST. KITTS...NEVIS...ANTIGUA...MONTSERRAT...ANGUILLA... AND BARBUDA
* SABA...ST. EUSTATIUS...AND ST. MAARTEN
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* BRITISH VIRGIN ISLANDS
* PUERTO RICO...VIEQUES...CULEBRA...AND THE U.S. VIRGIN ISLANDS
A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.
A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.
INTERESTS ELSEWHERE IN HISPANIOLA AND CUBA SHOULD MONITOR THE
PROGRESS OF ISAAC.
FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED
STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR LOCAL NATIONAL
WEATHER SERVICE FORECAST OFFICE. FOR STORM INFORMATION SPECIFIC TO
YOUR AREA OUTSIDE THE UNITED STATES...PLEASE MONITOR PRODUCTS
ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.
DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 500 PM AST...2100 UTC...THE CENTER OF TROPICAL STORM ISAAC WAS
LOCATED NEAR LATITUDE 15.4 NORTH...LONGITUDE 53.9 WEST. ISAAC IS
MOVING TOWARD THE WEST NEAR 17 MPH...28 KM/H...AND THIS GENERAL
MOTION IS EXPECTED TO CONTINUE FOR THE NEXT COUPLE OF DAYS. ON THE
FORECAST TRACK...THE CENTER OF ISAAC SHOULD MOVE THROUGH THE
CENTRAL LESSER ANTILLES WEDNESDAY EVENING...AND EMERGE OVER THE
EASTERN CARIBBEAN SEA BY THURSDAY MORNING.
REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INDICATE
THAT MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/H...WITH
HIGHER GUSTS. ADDITIONAL STRENGTHENING IS FORECAST DURING THE NEXT
48 HOURS.
TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 45 MILES...75 KM
TO THE NORTHEAST OF THE CENTER.
THE MINIMUM CENTRAL PRESSURE JUST MEASURED BY THE HURRICANE HUNTER
AIRCRAFT IS 1006 MB...29.71 INCHES.
HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE EXPECTED TO REACH THE WARNING
AREA BY WEDNESDAY AFTERNOON...MAKING OUTSIDE PREPARATIONS DIFFICULT
OR DANGEROUS.
RAINFALL...TOTAL RAIN ACCUMULATIONS OF 4 TO 8 INCHES ARE POSSIBLE
OVER THE NORTHERN WINDWARD ISLANDS AND THE LEEWARD ISLANDS. TOTAL
RAIN ACCUMULATIONS OF 1 TO 3 INCHES WITH MAXIMUM AMOUNTS OF 6
INCHES ARE POSSIBLE OVER PUERTO RICO AND THE VIRGIN ISLANDS.
STORM SURGE...A STORM SURGE WILL RAISE WATER LEVELS BY AS MUCH AS 1
TO 3 FEET ABOVE NORMAL TIDE LEVELS IN THE NORTHERN LEEWARD ISLANDS.
NEAR THE COAST...THE SURGE WILL BE ACCOMPANIED BY DANGEROUS WAVES.
SURF...DANGEROUS SURF AND RIP CURRENT CONDITIONS WILL AFFECT THE
WINDWARD AND LEEWARD ISLANDS DURING THE NEXT COUPLE OF DAYS. PLEASE
CONSULT PRODUCTS FROM YOUR LOCAL WEATHER OFFICE FOR MORE
INFORMATION.
NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...800 PM AST.
NEXT COMPLETE ADVISORY...1100 PM AST.
$$
FORECASTER BEVEN
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