[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 172357
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN AUG 17 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...
TROPICAL STORM FAY CENTERED NEAR 21.0N 80.3W OR ABOUT 175 NM...
330 KM...SOUTHEAST OF HAVANA CUBA AND ABOUT 230 NM...430 KM...
SOUTH-SOUTHEAST OF KEY WEST FLORIDA AT 18/0000 UTC MOVING SLOWLY
AND SOMEWHAT ERRATICALLY TOWARD THE WEST-NORTHWEST NEAR 9 KT...
17 KM/HR. A TURN TOWARD THE NORTHWEST IS EXPECTED TONIGHT...WITH
A TURN TOWARD THE NORTH EXPECTED MONDAY OR MONDAY NIGHT.  ON THE
FORECAST TRACK...FAY IS EXPECTED CROSS WESTERN CUBA OVERNIGHT
TONIGHT OR MONDAY MORNING...AND MOVE NEAR THE FLORIDA KEYS
MONDAY OR MONDAY NIGHT. ESTIMATED MINIMUM CENTRAL PRESSURE IS
1001 MB. MAXIMUM SUSTAINED WIND SPEED IS 45 KT WITH HIGHER
GUSTS. SLOW STRENGTHENING IS FORECAST DURING THE NEXT COUPLE OF
DAYS...AND FAY COULD BE APPROACHING HURRICANE STRENGTH WHEN IT
REACHES WESTERN CUBA TONIGHT AND WHEN IT APPROACHES THE FLORIDA
KEYS MONDAY OR MONDAY NIGHT. PLEASE SEE THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT1/WTNT21 KNHC
AND PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS MIATCPAT1/WTNT31
KNHC FOR MORE DETAILS. FAY HAS BECOME A LITTLE BETTER ORGANIZED
IN SATELLITE AND RADAR IMAGERY THIS EVENING...WITH INCREASED
CURVED BANDS OF CONVECTION NEAR THE CENTER IN THE NORTHEASTERN
SEMICIRCLE. FAY IS EXPECTED TO PRODUCE TOTAL RAINFALL
ACCUMULATIONS OF 4 TO 8 INCHES OVER MUCH OF CUBA...WITH ISOLATED
MAXIMUM AMOUNTS OF 12 INCHES. THESE RAINS COULD PRODUCE
LIFE-THREATENING FLASH FLOODS AND MUD SLIDES. RAINFALL
ACCUMULATIONS OF 1 TO 3 INCHES ARE POSSIBLE OVER GRAND CAYMAN
AND OVER THE CENTRAL BAHAMAS. HEAVY RAIN MAY BEGIN TO AFFECT THE
FLORIDA KEYS AND SOUTH FLORIDA TONIGHT AND INTO MONDAY.
RAINFALL TOTALS OF 4 TO 6 INCHES...WITH MAXIMUM AMOUNTS OF 10
INCHES ARE POSSIBLE FOR THE FLORIDA KEYS AND SOUTH FLORIDA.

...TROPICAL WAVES...
THE TROPICAL WAVE THAT WAS PREVIOUSLY ALONG 35W IS RELOCATED
FURTHER EAST ALONG 29W/30W BASED ON LATEST VIS SAT IMAGERY FOR
THE DAY AND A QSCAT PASS FROM AROUND 2000 UTC THAT SHOWED A
CYCLONIC TURNING ALONG THE WAVE AXIS NEAR 13N. THE WAVE SHOWS UP
VERY WELL ON THE TPW PRODUCT WITH A BROAD AREA OF DEEP LAYERED
MOISTURE. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS
BEHIND THE WAVE AXIS FROM 9N-12N BETWEEN 23W-28W. ISOLATED
MODERATE CONVECTION IS ALSO NOTED SPINNING NEAR 13N BETWEEN 28W
AND 31W.

A TROPICAL WAVE IS APPROACHING THE LESSER ANTILLES AND EXTENDS
FROM 21N57W TO 8N60W. THIS WAVE IS MOVING WEST 10-15 KT AND IS
INTERACTING WITH AN UPPER-LEVEL TROUGH THAT ENTERS THE NE
CARIBBEAN. A NARROW BAND OF MOISTURE IS AHEAD OF THE WAVE AXIS
PRODUCING SCATTERED SHOWERS OVER THE WINDWARD ISLANDS AND
COASTAL WATERS.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 15N17W 10N34W 7N45W 7N56W. MOST
OF THE CONVECTIVE ACTIVITY IS ASSOCIATED WITH THE TROPICAL WAVE
LOCATED NEAR 29W/30W. A CLUSTER OF MODERATE CONVECTION IS NEAR
7N29W...AND NEAR 9N52W.

...DISCUSSION...

THE GULF OF MEXICO...
AN UPPER-LEVEL HIGH CENTERED NOW OVER W-CENTRAL MEXICO EXTENDS A
RIDGE EWD OVER THE WESTERN HALF OF THE GULF REGION AND THE
YUCATAN PENINSULA WHILE A MID/UPPER-LEVEL TROUGH IS OVER THE SE
CONUS AND THE NE CORNER OF THE GULF. THIS PATTERN SHOULD ALLOW
T.S. FAY TO TURN MORE NORTHWARD AFTER 24 HR...BUT THERE REMAINS
SIGNIFICANT DISAGREEMENT BETWEEN THE COMPUTER MODELS ON HOW MUCH
OF A TURN WILL OCCUR. SEE SPECIAL FEATURES. THIS UPPER-LEVEL
TROUGH SUPPORTS A STATIONARY FRONTAL BOUNDARY THAT LIES OVER THE
N GULF STATES AND EXTENDS FROM S GEORGIA TO SE LOUISIANA TO S
TEXAS. PREFRONTAL ACTIVITY IS PRODUCING SCATTERED SHOWERS WITH
EMBEDDED TSTMS OVER THE GULF N OF 25N. AN OUTER RAINBAND FROM
T.S. FAY IS CURRENTLY AFFECTING SOUTH FLORIDA...THE KEYS AND
THE SE PORTION OF THE GULF. WEATHER CONDITIONS ARE EXPECTED TO
DETERIORATE OVER THE SE GULF TOMORROW AFTERNOON AS FAY EMERGES
FROM WESTERN CUBA. AT THE SURFACE...A RIDGE ANCHORED ON A WEAK
1016 MB HIGH SITUATED NEAR 27N88W DOMINATES THE AREA PRODUCING
SLY RETURN FLOW OF 10 TO 15 KT OVER THE WESTERN HALF OF THE
GULF. NELY WINDS ASSOCIATED WITH THE CYCLONIC CIRCULATION OF FAY
ARE ALREADY BLOWING OVER THE SE GULF AS NOTED ON SFC
OBSERVATIONS AND AN EARLIER ASCAT PASS.

THE CARIBBEAN SEA...
MAIN FEATURE IN THE CARIBBEAN SEA IS T.S. FAY LOCATED SOUTH OF
CENTRAL CUBA. NEW WATCHES AND WARNINGS WERE ISSUED AT 2100 UTC.
RAIN BANDS ASSOCIATED WITH FAY ARE AFFECTING E-CENTRAL
CUBA...THE BAHAMAS...SOUTH FLORIDA AND THE KEYS AND THE SE
PORTION OF THE GULF OF MEXICO WITH A FEEDER BAND BETWEEN HAITI
AND JAMAICA. SEE SPECIAL FEATURES ABOVE. ELONGATED UPPER LOW IS
OVER WESTERN TIP OF CUBA EXTENDING AN UPPER TROUGH SW THROUGH
THE FAR NW CARIBBEAN O THE N COAST OF HONDURAS NEAR ROATAN
ISLAND. THIS LOW IS FORECAST BY THE COMPUTER MODELS TO MOVE AS
AN INVERTED TROUGH OVER THE YUCATAN PENINSULA LATE MONDAY INTO
TUE. FAY REMAINS ON THE SOUTH SIDE OF A LOW/MID-LEVEL RIDGE
ANCHORED ON A HIGH CURRENTLY OVER THE SOUTH-CENTRAL BAHAMAS.
THIS RIDGE COVERS THE CENTRAL CARIBBEAN WHILE AN UPPER-LEVEL
TROUGH THAT EXTENDS FROM AN UPPER LOW NEAR 26N61W ENTERS THE NE
CARIBBEAN. SCATTERED MODERATE CONVECTION IS SEEN OVER COSTA RICA
AND PANAMA LIKELY DUE TO THE CLOSE PROXIMITY OF THE ITCZ.
ACCORDING TO THE OFFICIAL FORECAST TRACK...FAY IS EXPECTED CROSS
WESTERN CUBA OVERNIGHT TONIGHT OR MONDAY MORNING.

THE ATLANTIC OCEAN...
AS PREVIOUSLY MENTIONED...THERE IS SOME SHOWER AND TSTM ACTIVITY
OVER THE W ATLC W OF 70W AND THE BAHAMAS ASSOCIATED WITH THE
OUTER RAINBANDS OF T.S. FAY. FURTHER EAST...SCATTERED SHOWERS
AND ISOLATED TSTMS ARE SPINNING AROUND AN UPPER-LEVEL LOW
LOCATED NEAR 26N61W. UPPER DIFFLUENCE BETWEEN THIS UPPER LOW AN
AN UPPER-LEVEL HIGH TO THE E LOCATED NEAR 26N46 IS SUPPORTING A
CLUSTER OF MODERATE CONVECTION THAT COVERS FROM 23N-28N BETWEEN
52W-54W. A SFC TROUGH IS ANALYZED IN THAT AREA AND RUNS FROM
30N52W TO 23N56W. THIS TROUGH...24 HOURS AGO WAS PART OF THE
TROPICAL WAVE THAT IS NOW APPROACHING THE LESSER ANTILLES.
ANOTHER UPPER LEVEL LOW IS W OF THE CANARY ISLANDS NEAR 28N20W.
AT THE SURFACE...A 1024 MB HIGH CENTERED OVER THE CENTRAL
ATLANTIC NEAR 35N44W EXTENDS A RIDGE W TOWARDS BERMUDA AND THE W
ATLC.

$$
GR





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