Ana and TD 3 take aim at the Lesser Antilles
Tropical Storm Ana was born this morning, when the remnants of Tropical Depression Two made a comeback and organized into the first tropical storm of the 2009 Atlantic hurricane season. Ana is the latest first named storm of the season since Hurricane Andrew got its name on August 17, 1992. The two storms have some similarities, as Andrew formed in the same part of the ocean, and also struggled in its early days with high wind shear and dry air. Let's hope the similarities end there.
Ana is struggling this afternoon. After an modest burst of heavy thunderstorm activity prompted NHC to upgrade Ana to a tropical storm early this morning, Ana has run into strong upper-level winds from the west that are creating high wind shear. This shear was not forecast, and it is not clear how long it will last. The shear has acted to drive dry air into the core of Ana, destroying almost all of Ana's heavy thunderstorms. The low-level center of the storm is now exposed to view, something that often foreshadows the death of a storm. It is possible the shear will destroy Ana, and several models (the GFS and ECMWF) forecast this may be the case. However, the shear forecast calls for shear to drop into the low range, 5 - 10 knots, tonight through Tuesday. If the shear does drop as forecast, Ana should be able to moisten the atmosphere around it sufficiently to protest itself from the dry Saharan air that surrounds it (Figure 1). SSTs are 27°C today, and will increase to 28°C by Sunday. By the time Ana moves into the Bahamas, total ocean heat content rises steeply (Figure 2), and rapid intensification of Ana is possible, if the shear and dry air haven't disrupted the storm. The intensity forecast models, for the most part, predict a steady intensification of Ana to the threshold of hurricane strength five days from now. The HWRF model is on the strong side, predicting a Category 2 hurricane. The GFDL predicts a weak tropical storm five days from now, but that is because the model has Ana passing over the rugged terrain of Hispaniola, something the other models do not predict. In summary, the intensity forecast for Ana has higher than usual uncertainty, and I give equal chances that the storm will be a hurricane--or non-existent--four days from now.
Figure 1. Water vapor image from this morning showing the large area of dry, Saharan air surrounding Ana, and lying to the north of Tropical Depression Three. Image credit: NOAA/SSD
Tropical Depression Three forms, could be Bill later today
QuikSCAT data from this morning and satellite loops revealed that the tropical wave (90L) in the middle Atlantic has finally developed a well developed surface circulation and can be classified as Tropical Depression Three. Recent satellite imagery suggests that TD 3 may already be Tropical Storm Bill. Water vapor imagery (Figure 1) shows that TD 3's center consolidated a few hundred miles south of the dry air of the Saharan Air Layer (SAL). Thus, the storm should not be affected by dry air and dust as much as Ana has been. Ana may also act to moisten the atmosphere in front of TD 3, helping protect the storm from the SAL as it edges farther north over the the three days.
Figure 2. Heat content of the ocean, in kJ per square cm. Oceanic heat content steadily increases for Ana and TD 3 as they approach the Lesser Antilles Islands. Oceanic heat content levels of 90 kJ per square cm are frequently associated with rapid intensification of hurricanes. Image credit: University of Miami.
Wind shear is moderate, 15 knots, but is forecast to fall to 10 - 15 knots on days 2 - 5. Sea Surface Temperatures are about 27.5°C, and will remain in the 27.5 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow TD 3 to intensify steadily, and I expect the storm will be at hurricane strength by Wednesday, when it will be near the northern Lesser Antilles Islands. Most of our reliable intensity models strengthen TD 3 into a hurricane by Wednesday. Oceanic heat content (Figure 2) increases sharply just before the islands, so TD 3 could be intensifying rapidly as it moves through or just north of the Lesser Antilles on Thursday. TD 3 consolidated farther south than expected, so the track models calling for a more northerly path were probably incorrect. In particular, the ECMWF model, which had TD 3 turning sharply northwestward and missing the Lesser Antilles Islands, was probably much too far to the north in this morning's 00Z run. TD 3 will probably pass very close to the northern Lesser Antilles islands on Wednesday and Thursday.
I'll have an update Sunday.
Jeff Masters
Reader Comments
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they're gonna shift, but as to how much, still dont know
Several believe they are...but who knows.
Unfortunately the loop current eddy can resupply warm waters pretty quickly.
If this bickering continues, I may want to become a volcanologist.
it's good to be persistent in life .. as I say .. if life is not smiles .. you have to tickle.
Are you making any preps?
So much for the downcasts on here about it....glad the man is alive.
Quoting thelmores:
You have to look at it in relation to its surrounding pressure as well...... pressure gradient. Not just the actual pressure.
So while 1013mb may not be impressive, it may be a little more quantitatively than normal.
I bet Drak will be impressed! quantitatively! LOL
thelmores is right. It's imbeded in an area of 1017+ mb...pressure gradient makes the wind.
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i have to agree. its just like tropical systems in the pacific. because the pacific has a lower ambient (sp?) pressure, a TC with a pressure of 1000 mb will most likely be weaker than a TC in the atlantic with a 1000 mb pressure. the reason is because the atlantic overall has higher initial pressures.
Level Geo. Height Air Temp. Dew Point Wind Direction Wind Speed
1012mb (29.88 inHg) Sea Level (Surface) 28.6°C (83.5°F) Approximately 23°C (73°F) 215° (from the SW) 5 knots (6 mph)
1000mb 108m (354 ft) 27.6°C (81.7°F) Approximately 23°C (73°F) 235° (from the SW) 6 knots (7 mph)
925mb 794m (2,605 ft) 21.4°C (70.5°F) 19.3°C (66.7°F) 240° (from the WSW) 7 knots (8 mph)
850mb 1,524m (5,000 ft) 18.0°C (64.4°F) Approximately 13°C (55°F) 225° (from the SW) 9 knots (10 mph)
700mb 3,165m (10,384 ft) 9.8°C (49.6°F) Approximately -4°C (25°F) 85° (from the E) 18 knots (21 mph)
500mb 5,880m (19,291 ft) -4.1°C (24.6°F) Approximately -22°C (-8°F) 30° (from the NNE) 8 knots (9 mph)
400mb 7,600m (24,934 ft) -14.9°C (5.2°F) Approximately -36°C (-33°F) 45° (from the NE) 9 knots (10 mph)
300mb 9,710m (31,857 ft) -30.9°C (-23.6°F) Approximately -51°C (-60°F) 95° (from the E) 11 knots (13 mph)
250mb 10,980m (36,024 ft) -40.9°C (-41.6°F) Approximately -57°C (-71°F) 135° (from the SE) 18 knots (21 mph)
200mb 12,460m (40,879 ft) -53.1°C (-63.6°F) Approximately -70°C (-94°F) 100° (from the E) 27 knots (31 mph)
150mb 14,260m (46,785 ft) -65.3°C (-85.5°F) Reading usually unavailable when air temperature is below -40°C (-40°F) 130° (from the SE) 24 knots (28 mph)
Hope they fly 91L soon, it's moved enough away from shore I don't have the surface obs I've had for 2 days.
Lightning here is shakin the house..
1. A LARGE AREA OF CLOUDINESS AND THUNDERSTORMS OVER THE SOUTHEASTERN
GULF OF MEXICO IS PRIMARILY ASSOCIATED WITH A TROPICAL WAVE
INTERACTING WITH A MID- TO UPPER-LEVEL TROUGH. THIS ACTIVITY HAS
BECOME A LITTLE MORE CONCENTRATED OVER THE SOUTHEASTERN GULF OF
MEXICO WHERE SURFACE PRESSURES ARE BEGINNING TO FALL. THERE ARE NO
SIGNS OF A SURFACE CIRCULATION AT THIS TIME AND ANY ADDITIONAL
DEVELOPMENT...IF ANY...SHOULD BE SLOW TO OCCUR. THIS SYSTEM SHOULD
MOVES TOWARD THE NORTHWEST OVER THE EASTERN GULF OF MEXICO ON
SUNDAY. THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
Which way is 91L moving?
I would say a low tropical storm....it could be more or less.
August 24 , if bill hits, it hits August 23
Personally, I would rather go to war with a battle tested Sgt Major then a 1st LT fresh out of West Point. My cred for that comment. My father served 26 yrs US Army. Served two tours in Korea one in Nam, Ran two Platoons in Europe During the Cold War and Taught at West Point.
So please stick to the weather.
It is getting really nasty around us Skye....wasn't anticipating this weather tonight.
OH well... we'll know tomorrow.
August 18th in Palm Beach County
All I had to do was update my hurricane kit and make sure I had a plan. I still dont have a wireless radio though.
91L is rotating nicely...
I think Northwest, bringing it to the Florida panhandle area I believe.
For a few days I've stuck with a TD or TS wouldn't suprise me. This lightning..I'll go outside chance of a Cat 1.
its rather a waste of blog space it such a time info needs to be communicated.
IMO, I have been saying this since Bill was 90L. Tracks are going to shift as along as it does two things:
continue west
speed up
Bill is now moving wsw or 260.
Now recurve the storm as the models do, it still leaves about 1-2 degrees lat which when extrapolated 5 days out is a very large error. I dont buy some of the models since they had Bill moving west northwest (where it is suppose to be). I'm still not a 100 percent sure on this, so it remains a watch and see but so far Bill has not turn north.
This is a TD, at least.
yeah, kinda does....not sure if it actually is or not though.
PcolaDan 1:27 AM GMT on August 16, 2009
thanks to the both of you for answering my questions.. very helpful :)
and i do agree going to war with a season vet is makes you feel so much more safer then doing it with a rookie!
i have nothing intelligent to say about the weather and storms other then it rained like crazy earlier here due to 91L i'm hoping that it doesn't blow up more and is only a heavy rain producer where ever it may go good luck and godspeed to anyone in the path of any of these storms!
MARK
14.4N/49.7W
03L/TS/BILL
MARK
10.9N/35.7W
AOI/INV/91L
MARK
25.1N/82.3W
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