[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 192324
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT WED AUG 19 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2230 UTC.

...SPECIAL FEATURES...
HURRICANE BILL REMAINS A CATEGORY FOUR HURRICANE ON THE
SAFFIR-SIMPSON SCALE WITH MAXIMUM SUSTAINED WINDS SPEEDS OF 115
KT WITH GUSTS UP TO 140 KT. THE CENTER OF HURRICANE BILL WAS
LOCATED NEAR 19.8N 57.6W OR ABOUT 335 MILES...535 KM...NE OF THE
LEEWARD ISLANDS AND ABOUT 970 MILES...1565 KM...SSE OF BERMUDA
MOVING NW NEAR 17 KT. THE ESTIMATED CENTRAL PRESSURE IS 947 MB.
BILL IS A LARGE SYSTEM WITH HURRICANE FORCE WINDS EXTENDING
OUTWARD FROM THE CENTER UP TO 85 MILES...140 KM...AND WITH
TROPICAL STORM FORCE WINDS EXTENDING OUTWARD UP TO 230
MILES...370 KM. ADDITIONAL STRENGTHENING IS POSSIBLE DURING THE
NEXT COUPLE OF DAYS. LARGE SWELLS ASSOCIATED WITH BILL WILL
START TO IMPACT ISLANDS IN THE NE CARIBBEAN DURING THE NEXT DAY
OR TWO...AND WILL BEGIN TO AFFECT BERMUDA AND PORTIONS OF THE E
COAST OF THE UNITED STATES FRIDAY AND SATURDAY. PLEASE READ THE
LATEST FORECAST/ ADVISORY UNDER AWIPS/WMO HEADERS TCMAT3/WTNT23
KNHC FOR MORE DETAILS. NUMEROUS MODERATE/STRONG CONVECTION IS
FROM 18N-21N BETWEEN 55W-60W. NUMEROUS MODERATE/SCATTERED STRONG
CONVECTION IS FROM 22N-25N BETWEEN 53W-59W.

...TROPICAL WAVES...
A TROPICAL WAVE IS APPROACHING THE CAPE VERDE ISLANDS EXTENDING
FROM 15N22W TO 9N19W MOVING W NEAR 10 KT. THIS WAVE COINCIDES
WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL
PRECIPITABLE WATER IMAGERY. SATELLITE DERIVED WINDS ALSO
INDICATE LOW/MID-LEVEL CYCLONIC FLOW IN THE VICINITY OF THE WAVE
AXIS. NO DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE WAVE.

A TROPICAL WAVE EXTENDS FROM 15N46W TO 8N43W MOVING W NEAR 20
KT. THIS WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. SATELLITE IMAGERY
INDICATES AN INVERTED-V STRUCTURE IN THE LOW-LEVEL CLOUDS.
SATELLITE DERIVED WINDS ALSO INDICATE CYCLONIC TURNING IN THE
VICINITY OF THE WAVE AXIS. A DRY SAHARAN AIR LAYER LIES TO THE E
OF THE WAVE AXIS INHIBITING ANY DEEP CONVECTION.

A TROPICAL WAVE IS ALONG 84W S OF 19N MOVING W NEAR 15 KT. THIS
WAVE ORIGINATED AS THE REMNANTS OF ANA THAT DISSIPATED A FEW
DAYS AGO. THIS WAVE LIES UNDER A DIFFLUENT ZONE ALOFT WHICH IS
ENHANCING SCATTERED MODERATE/ISOLATED STRONG CONVECTION ACROSS
CENTRAL AMERICA FROM 8N-17N BETWEEN 78W-86W.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 12N15W 10N30W 12N43W 9N48W
12N56W 10N61W. SCATTERED MODERATE/STRONG CONVECTION IS JUST
INLAND OVER AFRICA FROM 10N-13N BETWEEN 13W-16W. A CLUSTER OF
SCATTERED MODERATE/STRONG CONVECTION IS FROM 11N-12N BETWEEN
24W-26W. ISOLATED MODERATE CONVECTION IS WITHIN 150 NM N AND 200
NM S OF THE AXIS BETWEEN 22W-32W.

...DISCUSSION...

THE GULF OF MEXICO...
A WEAK SURFACE RIDGE IS ACROSS THE GULF OF MEXICO TONIGHT.
HOWEVER...SHOWERS/THUNDERSTORMS ARE AFFECTING MUCH OF THE BASIN
DUE TO UPPER LEVEL FEATURES. ISOLATED SHOWERS/THUNDERSTORMS ARE
ACROSS THE NRN GULF N OF 28N BETWEEN 85W-96W ENHANCED BY UPPER
LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE ACROSS THE ERN
CONUS FROM VIRGINIA TO AN UPPER LEVEL HIGH S OF LOUISIANA NEAR
28N92W AND AN UPPER LEVEL TROUGH ACROSS THE CENTRAL CONUS.
SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS THE W FLORIDA COAST N
OF 27N E OF 84W DUE TO UPPER LEVEL DIFFLUENCE BETWEEN THE RIDGE
ACROSS THE NRN GULF/ERN CONUS AND AN UPPER LEVEL TROUGH ACROSS
THE W ATLC. SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO ACROSS NW
CUBA FROM 22N-24N BETWEEN 81W-83W INTO THE STRAITS OF
FLORIDA...AND ACROSS THE YUCATAN PENINSULA FROM 18N-21N BETWEEN
88W-91W. THIS ACTIVITY IS ENHANCED BY UPPER LEVEL DIFFLUENCE
BETWEEN THE HIGH IN THE NW GULF AND AN UPPER LEVEL LOW E OF THE
YUCATAN PENINSULA NEAR 19N86W. EXPECT A TROPICAL WAVE ALONG 84W
TO REACH THE YUCATAN PENINSULA TONIGHT AND TO MOVE INTO THE SW
GULF S OF 20N THU.

THE CARIBBEAN SEA...
A TROPICAL WAVE ALONG 84W IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS ACROSS THE SW CARIBBEAN AND CENTRAL
AMERICA FROM 8N-17N BETWEEN 78W-86W. THIS ACTIVITY IS ENHANCED
BY UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER LEVEL LOW E OF THE
YUCATAN PENINSULA NEAR 19N86W AND AN UPPER LEVEL HIGH OVER
COLUMBIA NEAR 11N74W. A FEW ISOLATED SHOWERS/POSSIBLE
THUNDERSTORMS OVER OVER THE E DOMINICAN REPUBLIC FROM 18N-19N
BETWEEN 69W-70W. THIS ACTIVITY IS MOST LIKELY DUE TO DAYTIME
HEATING AND INSTABILITY...AS THE AREA IN UNDER STRONG SUBSIDENCE
ALOFT. THE REMINDER OF THE CARIBBEAN IS EXPERIENCING GENERALLY
FAIR WEATHER UNDER THE INFLUENCE OF A DRY SAHARAN AIR LAYER AND
STRONG SUBSIDENCE ALOFT. FRESH TO STRONG TRADEWINDS ARE ACROSS
MUCH OF THE BASIN WITH THE HIGHEST WINDS NEAR THE COAST OF
COLUMBIA. LARGE SWELLS ASSOCIATED WITH MAJOR HURRICANE BILL WILL
BEGIN IMPACTING ISLANDS ACROSS THE NE CARIBBEAN IN THE NEXT DAY
OR TWO.

THE ATLANTIC OCEAN...
ISOLATED SHOWERS/POSSIBLE THUNDERSTORMS ARE ACROSS THE FAR W
ATLC N OF 27N W OF 78W. THIS ACTIVITY IS ENHANCED BY UPPER LEVEL
DIFFLUENCE BETWEEN AN UPPER LEVEL RIDGE OVER THE ERN CONUS AND
AN UPPER LEVEL TROUGH ACROSS THE W ATLC WITH AXIS ALONG 72W. A
SURFACE TROUGH ENTERS THE DISCUSSION AREA NEAR 31N42W EXTENDING
TO 29N55W. NO SHOWERS ARE CURRENTLY ASSOCIATED WITH THE TROUGH.
THE REMAINDER OF THE ATLC...BESIDES HURRICANE BILL...SEE
ABOVE...IS DOMINATED BY A BROAD SURFACE RIDGE ANCHORED BY A 1021
MB HIGH NEAR 32N71W...AND A 1024 MB HIGH NEAR 32N32W. IN THE
UPPER LEVELS...AN UPPER LEVEL RIDGE IS OVER THE CENTRAL ATLC E
OF THE UPPER TROUGH IN THE W ATLC WITH AN UPPER LEVEL HIGH
CENTERED NEAR 28N31W. AN UPPER LEVEL TROUGH IS ACROSS THE FAR E
ATLC N OF 23N WITH AXIS ALONG 23W.

$$
WALTON



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