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
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And at the same time, setting the stage to supply Ana with some more moisture right when she needs it. It almost seems like these two are colluding against us.
In Doral also
UW - CIMSS
ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm
----- Current Analysis -----
Date : 15 AUG 2009 Time : 194500 UTC
Lat : 11:25:54 N Lon : 35:06:30 W
CI# /Pressure/ Vmax
2.5 /1005.0mb/ 35.0kt
Final T# Adj T# Raw T#
(3hr avg)
2.5 2.8 3.2
Latitude bias adjustment to MSLP : 0.0mb
Center Temp : -0.4C Cloud Region Temp : -33.4C
Scene Type : SHEAR (0.15^ TO DG)
Positioning Method : FORECAST INTERPOLATION
Ocean Basin : ATLANTIC
Dvorak CI > MSLP Conversion Used : ATLANTIC
Tno/CI Rules : Constraint Limits : 0.2T/hour
Weakening Flag : OFF
Rapid Dissipation Flag : OFF
****************************************************
not me! wonder why! :rolleyes:
models = guesses
might as well grab the bookie...
We just got ours a few mins. ago in Kendall..
Bill's arm - a fairly well organize system with outer convective rings around a define center
Boom=Ana?
Boom=Bill?
Pow=GoM disturbance?
Yup, count me in on those worried. We'll see what happens. I'm prepared for a direct hit from any of those 3 systems just in case. Hopefully we'll be spared once again.
AT 5 PM AST...2100 UTC...THE GOVERNMENT OF THE NETHERLAND ANTILLES
HAS ISSUED A TROPICAL STORM WATCH FOR ST. MAARTEN...SABA...AND ST.
EUSTATIUS. A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM
CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN
36 HOURS.
FORMS IN THE FAR EASTERN ATLANTIC...
...SUMMARY OF 500 PM AST INFORMATION...
LOCATION...11.3N 35.2W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 265 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1004 MB
DUTCH LEEWARD ISLANDS
they are in our area
Miami, Base Reflectivity 0.50 Degree Elevation Range 248 NMI
Hello, Bill.
ATLANTIC HAS CONTINUED TO BECOME BETTER ORGANIZED. THE CYCLONE IS
LARGE AND HAS NUMEROUS CYCLONICALLY-CURVED CONVECTIVE BANDS WITH
THE OUTFLOW PRIMARILY ON THE WESTERN SEMICIRCLE.
anybody?... I know someone knows this in here...
synth
That's true Jurakan. Just trying to stay positive, even when right now it looks pretty grim. If it's not Ana then it's Bill or what could end up being Claudette... who knows. :-s
Yes, it has...another one that may need to be watched in the GOM...
so has Bill
That is if it can survive Hispaniola and Cuba.
True, but then it could just skirt them as well.
What type of preparation has your island taken with the two possible threats so close together?
Also, this will go lot more West..I am believing 12z UKMET model which takes in South of PR towards Jamaica...ot thereabouts!
We shall see...what do you guys think?
he's a fighter. She survived strong shear and a lot of dry air. People counted her out and she's back.
In an anomalous years like this one, is it possible that the "persistence" factor may preclude any modeling data or expected meteorlogical prognostication tools?
Just trying to make sense of low TC year with such high SST's in the Atlantic Basin
Viewing: 1101 - 1151
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