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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Good morning everyone..
What does the "M" mean on the tracking from NHC?
Exactly. People forget between seasons that storms in specific and weather in general both have a pattern of behaving unexpectedly.
Dont ever take your eye off of anything in ther gulf.
Yup.
Major hurricane.
Wind speed is greater than 110 - see the table describing the chart
Major hurricane
The key tells you it means Major Hurricane
Major Hurricane
I would say WNW, just looks like he's becoming more symmetric to the north. He's had a flattop the last couple days.
WHXX01 KWBC 161309
CHGHUR
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1309 UTC SUN AUG 16 2009
DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.
ATLANTIC OBJECTIVE AIDS FOR
TROPICAL CYCLONE BILL (AL032009) 20090816 1200 UTC
...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
090816 1200 090817 0000 090817 1200 090818 0000
LAT LON LAT LON LAT LON LAT LON
BAMS 11.9N 37.7W 12.8N 40.8W 13.6N 44.0W 14.2N 46.9W
BAMD 11.9N 37.7W 12.8N 40.4W 13.8N 43.2W 14.9N 45.9W
BAMM 11.9N 37.7W 12.6N 40.9W 13.2N 44.1W 13.9N 47.0W
LBAR 11.9N 37.7W 12.5N 40.4W 13.3N 43.6W 14.0N 46.8W
SHIP 50KTS 59KTS 69KTS 77KTS
DSHP 50KTS 59KTS 69KTS 77KTS
...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
090818 1200 090819 1200 090820 1200 090821 1200
LAT LON LAT LON LAT LON LAT LON
BAMS 14.7N 49.6W 16.7N 54.4W 20.3N 59.9W 23.5N 64.4W
BAMD 15.9N 48.6W 18.5N 53.7W 21.8N 58.6W 25.9N 62.6W
BAMM 14.5N 49.6W 16.6N 54.1W 20.3N 58.9W 24.1N 63.2W
LBAR 14.4N 50.1W 16.0N 56.2W 19.7N 60.2W 23.7N 63.5W
SHIP 85KTS 98KTS 97KTS 91KTS
DSHP 85KTS 98KTS 97KTS 91KTS
...INITIAL CONDITIONS...
LATCUR = 11.9N LONCUR = 37.7W DIRCUR = 285DEG SPDCUR = 11KT
LATM12 = 11.2N LONM12 = 35.5W DIRM12 = 279DEG SPDM12 = 10KT
LATM24 = 11.5N LONM24 = 33.3W
WNDCUR = 50KT RMAXWD = 60NM WNDM12 = 35KT
CENPRS = 997MB OUTPRS = 1011MB OUTRAD = 200NM SDEPTH = D
RD34NE = 120NM RD34SE = 120NM RD34SW = 60NM RD34NW = 90NM
$$
NNNN
Bill strengthens. Around 55mph.
Also dropped 5mb.
It's on the path...
I guess the "M" means Major Hurricane
this will be the one I will be watching..that cone dosent look like a recurve to me..in fact it look like it dropped south since the 11:00 advisory last night
Claudette by 11am
M = Major Hurricane
Closest buoy to TD4. The low is about a 1012 mb. Strongest winds (25 kt) displaced to the NW of the centre by about 50 mi. Link
...The ENSO climate cycle can displace the subtropical ridge, with La Niñas allowing for a more northerly axis for the ridge, while El Niños show flatter, more southerly ridges....
...In the Atlantic basin, the subtropical ridge position tends to lie about 5 degrees farther south during El Niño years, which leads to a more southerly recurvature for tropical cyclones during those years....
MJO
lol
just before making the over predicted Northward recurvature
which may not take place at all without help from HAARP.
The Highs orientation is wrong and the troughs movement is
over done in virtually every model so far.
if the highs were to bridge on the backside of the trough
bill may get trapped which could make for a slightly different
forecast late next week
Cat5 Bill in 120 hours might be a watcher.
Alberto always come in mind when someone "blows off" a storm... the GOM turned blood red.... it was freakish!
Viewing: 4601 - 4651
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