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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TTAA00 KNHC DDHHMM
BULLETIN
TROPICAL STORM BILL ADVISORY NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL032009
1100 PM AST SAT AUG 15 2009
...BILL MOVING WESTWARD OVER THE FAR EASTERN ATLANTIC...
AT 1100 PM AST...0300 UTC...THE CENTER OF TROPICAL STORM BILL WAS
LOCATED NEAR LATITUDE 11.3 NORTH...LONGITUDE 36.6 WEST OR ABOUT 905
MILES...1460 KM...WEST-SOUTHWEST OF THE CAPE VERDE ISLANDS.
BILL IS MOVING TOWARD THE WEST NEAR 16 MPH...26 KM/HR...AND THIS
MOTION WITH A GRADUAL TURN TO THE WEST-NORTHWEST IS EXPECTED DURING
THE NEXT 24 TO 48 HOURS.
MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/HR...WITH HIGHER
GUSTS. SOME STRENGTHENING IS FORECAST AND BILL IS FORECAST TO
BECOME A HURRICANE DURING THE NEXT FEW DAYS.
TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 70 MILES...110 KM
FROM THE CENTER.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 1004 MB...29.65 INCHES.
...SUMMARY OF 1100 PM AST INFORMATION...
LOCATION...11.3N 36.6W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1004 MB
THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
500 AM AST.
$$
FORECASTER AVILA
NNNN
LOCATION...11.3N 36.6W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1004 MB
You are correct about COC.
Jamaica
This is one of the copious amounts of reasons why I hesitate to blog in here anymore.
"...THE ONLY DYNAMICAL MODELS
THAT KEEP ANA ARE THE UK AND THE NOGAPS. THE REST OF THEM WEAKEN
ANA TO A TROPICAL WAVE. I AM TEMPTED TO SHOW WEAKENING BUT FOR
NOW...I AM GOING TO FOLLOW THE PREVIOUS FORECAST AND SHIPS MODEL
GUIDANCE. THE OFFICIAL FORECAST SHOWS SLOW STRENGTHENING THROUGH 48
HOURS FOLLOWED BY WEAKENING AS THE CYCLONE INTERACTS WITH
HISPANIOLA AND CUBA."
...SUMMARY OF 1100 PM AST INFORMATION...
LOCATION...11.3N 36.6W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1004 MB
im almost speechless xD
I hit that
;=)
Agree
..waves at IKE!
well this is a first, looks like NOAHH is forecasting against the latest model runs =O
waves back:)
that dosent look like "much" of a recurvature..
... Fast moving line of strong showers and thunderstorms moving
across Lake... Orange... Seminole... and northern Brevard counties...
At 1005 PM EDT... National Weather Service Doppler radar indicated a
line of strong storms from Cape Canaveral to 9 miles south of
Clermont... moving north at 25 mph.
This line of strong showers and storms will move through
Lake... Orange... Seminole... Volusia counties with gusty winds of 45
to 55 mph. These winds can cause unsecured objects to blow
around... snap tree limbs or cause power outages. Occasional cloud to
ground lightning strikes can also be expected.
Torrential rainfall can be expected... causing temporary ponding on
some roads and minor flooding of poor drainage areas."
Getting closer. When a storm is approaching I listen for the thunder first (a common occurrence where I live), but sometimes what I hear is the basso profundo coming from someone's car speakers or the guy next door starting his Harley!
And building an ark.
Not so sure about that, but we shall see. Everyone writing off Ana yet again. Tropics can change fast......very fast. So do not call Ana dead yet.
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