[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 200553
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT THU AUG 20 2009

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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0415 UTC.

...SPECIAL FEATURES...
HURRICANE BILL IS CENTERED NEAR 20.7N 58.9W OR ABOUT 275 NM NE
OF THE LEEWARD ISLANDS AND ABOUT 765 NM SSE OF BERMUDA MOVING NW
AT 15 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 945 MB. MAXIMUM
SUSTAINED WIND SPEED IS 115 KT WITH GUSTS TO 140 KT. SEE THE
LATEST FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS TCMAT3/WTNT23
KNHC FOR MORE DETAILS. HURRICANE BILL DISPLAYED A WELL DEFINED
EYE WITH SCATTERED STRONG CONVECTION WITHIN 90 NM OF THE CENTER
IN THE SW QUADRANT AND SCATTERED MODERATE/ISOLATED STRONG
CONVECTION COVERING THE REMAINDER OF THE AREA FROM 18N-24N
BETWEEN 55W-61W.

...TROPICAL WAVES...
TROPICAL WAVE IS ALONG 22W S OF 16N MOVING W 10 KT. WAVE IS AT
THE LEADING EDGE OF AN AREA DEEP LAYER MOISTURE MAXIMUM OBSERVED
IN TOTAL PRECIPITABLE WATER IMAGERY AND IS CLEARLY DEFINED
MAINLY IN THE LOW/MID LEVELS. HOWEVER...DUE TO DRY UPPER AIR
THERE IS NO ASSOCIATED CONVECTION WITH POSSIBLE ISOLATED
SHOWERS 90 NM OF THE WAVE AXIS.

TROPICAL WAVE REMAINS SLIGHTLY TILED DUE TO HURRICANE BILL
EXTENDING FROM 15N46W TO 8N44W MOVING W 15-20 KT. WAVE IS
CLEARLY EMBEDDED WITHIN AN AREA DEEP LAYER MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY AND IS WELL DEFINED
IN THE LOW/MID LEVELS. HOWEVER...DUE TO DRY UPPER AIR THERE IS
NO ASSOCIATED SHOWERS/CONVECTION.

TROPICAL WAVE IS ALONG 85W/86W S OF 19N MOVING W 10-15 KT. WAVE
IS CLEARLY DEFINED IN THE E PACIFIC REGION BUT DUE TO DRY STABLE
AIR OVER THE CARIBBEAN IS NOT PRODUCING ANY SHOWERS/CONVECTION
IN THE ATLC/CARIBBEAN BASIN.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 13N15W 12N24W 9N33W 13N43W
10N49W 11N56W 9N62W. CLUSTERS OF SCATTERED MODERATE/ISOLATED
STRONG CONVECTION ARE WITHIN 60/75 NM OF LINE FROM 8N30W 5N37W.
CLUSTERS OF SCATTERED MODERATE CONVECTION ARE INLAND AND WITHIN
60/75 NM ALONG THE COAST OF W AFRICA BETWEEN 8N-13N. SMALL
CLUSTERS OF SIMILAR CONVECTION ARE WITHIN 75 NM OF THE ITCZ AXIS
BETWEEN 24W-35W.

...DISCUSSION...

GULF OF MEXICO...
BROAD UPPER RIDGE EXTENDS FROM OVER MEXICO NEAR TUXPAN NNE TO
OVER THE LOWER MISSISSIPPI VALLEY TO THE CAROLINAS WHILE A UPPER
LOW IN THE CARIBBEAN EXTENDS AN UPPER TROUGH OVER THE REMAINDER
OF THE GULF. THE SURFACE RIDGE FROM THE W ATLC IS CONTINUES TO
BUILD ACROSS THE N GULF WITH A WEAKENING SURFACE TROUGH
EXTENDING FROM 28N96W TO NW YUCATAN. SCATTERED SHOWERS/
THUNDERSTORMS ARE N OF ERN CUBA WITHIN 30/45 NM OF LINE FROM
24N83W TO 23N85W. ISOLATED SHOWERS CONTINUE TO DOT THE REMAINDER
OF THE GULF MAINLY WITHIN N OF 27N AND WITHIN 120 NM OF THE
SURFACE TROUGH.

CARIBBEAN SEA...
AN UPPER LOW IS CENTERED JUST OFF THE YUCATAN NEAR 19N86W
COVERING THE NW CARIBBEAN AND EXTENDING AN UPPER TROUGH N OVER
THE E GULF OF MEXICO. AN UPPER RIDGE EXTENDS FROM E PANAMA ALONG
79W N TO 15N PROVIDING UPPER LEVEL DIFFLUENCE TO GENERATE
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS S OF 12N W OF 75W FROM
COLOMBIA TO CENTRAL AMERICA. SCATTERED SHOWERS AND POSSIBLE
ISOLATED THUNDERSTORMS ARE OBSERVED OVER S HAITI AND WITHIN 60
NM ALONG THE COAST IN THE ADJACENT COASTAL WATERS. FRESH TO
STRONG EASTERLY TRADE WINDS CONTINUE ACROSS THE AREA. DRY STABLE
AIR IS ACROSS THE REMAINDER OF THE AREA E OF 80W LIMITING ANY
DEEP LAYERED SHOWERS. HOWEVER...FAST LOW LEVEL ISOLATED SHOWERS
ARE ACROSS THE E CARIBBEAN E OF 69W WITH SCATTERED SHOWERS AND
POSSIBLE ISOLATED THUNDERSTORMS MOVING SW AS WELL AS HIGHER SEAS
AND SWELLS ACROSS THE LEEWARD ISLANDS TO PUERTO RICO ALL
COMPLIMENTS OF HURRICANE BILL AS IT CONTINUES TO MOVE NW OF THE
ISLANDS.

ATLANTIC OCEAN...
THE MAIN FOCUS THIS MORNING FOR THE ATLC IS HURRICANE BILL.
SCATTERED SHOWERS/ISOLATED THUNDERSTORMS LINGER OFF THE COAST OF
FLORIDA FROM 25N-31N BETWEEN 79W-80W. THE NARROW UPPER TROUGH
EXTENDS THROUGH 32N70W TO THE BAHAMAS NEAR 25N76W PROVIDING
SUPPORT FOR A SURFACE TROUGH THAT EXTENDS FROM 31N64W TO 28N66W
GENERATING SCATTERED SHOWERS/ISOLATED THUNDERSTORMS FROM 28N-31N
BETWEEN 65W-68W. OTHERWISE THE ATLC BASIN IS DOMINATED BY A
SURFACE RIDGE ANCHORED IN THE W ATLC BY A 1021 MB HIGH BETWEEN
BERMUDA AND NORTH CAROLINA COAST AND BY A 1025 MB HIGH S OF THE
AZORES WITH A WEAKNESS OVER THE CENTRAL ATLC DUE TO HURRICANE
BILL.

$$
WALLACE



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