[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 220002
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...
AS OF 0000 UTC...HURRICANE BILL IS CENTERED NEAR 30.2N 67W OR
ABOUT 200 MILES...325 KM...SW OF BERMUDA AND ABOUT 600
MILES...970 KM...ESE OF CAPE HATTERAS NORTH CAROLINA MOVING NNW
NEAR 17 KT. MAXIMUM SUSTAINED WIND SPEEDS ARE 90 KT WITH GUSTS
TO 110 KT. BILL IS A CATEGORY TWO HURRICANE ON THE
SAFFIR-SIMPSON SCALE. SOME STRENGTHENING IS POSSIBLE TONIGHT OR
SATURDAY. TROPICAL STORM FORCE WINDS ARE ALREADY OBSERVED IN
BERMUDA. A TROPICAL STORM WARNING AND HURRICANE WATCH REMAIN IN
EFFECT FOR BERMUDA. HURRICANE FORCE WINDS EXTEND OUTWARD UP TO
85 MILES...140 KM...FROM THE CENTER...AND TROPICAL STORM FORCE
WINDS EXTEND OUTWARD UP TO 275 MILES...445 KM. LARGE SWELLS
GENERATED BY HURRICANE BILL ARE AFFECTING THE BAHAMAS AND
BERMUDA...AND BEGINNING TO AFFECT THE SOUTHEAST COAST OF THE
UNITED STATES. LARGE SWELLS WILL BEGIN TO AFFECT MUCH OF THE
REMAINDER OF THE U.S. EAST COAST AND THE ATLANTIC MARITIMES OF
CANADA DURING THE NEXT DAY OR TWO. THESE SWELLS WILL LIKELY CAUSE
EXTREMELY DANGEROUS SURF AND LIFE-THREATENING RIP CURRENTS. SEE
THE LATEST FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
TCMAT3/WTNT23 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION
IS WITHIN 100 NM FROM THE CENTER OF BILL...WITH MODERATE
CONVECTION EXTENDING OUT TO 150 NM...WITHIN 200 NM IN A RAINBAND
TO THE NE OF THE CENTER.

...TROPICAL WAVES...
A NEW TROPICAL WAVE IS ADDED TO THE 1800 UTC SURFACE ANALYSIS
ALONG 20W S OF 16N MOVING W NEAR 15 KT. THIS WAVE COINCIDES WITH
A DEEP LAYER MOISTURE MAXIMUM OBSERVED IN TOTAL PRECIPITABLE
WATER IMAGERY. THIS WAVE IS LOW-AMPLITUDE DUE TO A LAYER OF DRY
SAHARAN AIR N OF 16N. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS FROM 9N-11N BETWEEN 20W-23W.

A TROPICAL WAVE IS ALONG 32W S OF 17N MOVING W NEAR 15 KT. THIS
WAVE IS RELOCATED FARTHER W THAN ITS CURRENT MOTION IMPLIES IN
ORDER TO ALIGN WITH A 1010 MB LOW-LEVEL SURFACE CIRCULATION NEAR
12N32W NOTED IN CURRENT SATELLITE IMAGERY. THE WAVE COINCIDES
WITH A DEEP LAYERED MOISTURE MAXIMUM OBSERVED IN THE TOTAL
PRECIPITABLE WATER IMAGERY. ISOLATED MODERATE CONVECTION IS FROM
13N-15N BETWEEN 32W-25W.

A TROPICAL WAVE IS ALONG 57W S OF 16N MOVING W NEAR 15 KT. THIS
WAVE LIES IN A BROAD AREA OF DEEP LAYER MOISTURE OBSERVED IN
TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE CONVECTION
IS WITHIN THE ITCZ AXIS FROM 8N-12N BETWEEN 55W-61W.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 13N13W 11N23W 13N31W 9N45W
9N61W. A LARGE CLUSTER OF NUMEROUS STRONG CONVECTION IS
APPROACHING THE AFRICA COAST FROM 13N-18N BETWEEN 10W-17W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN 150 NM S
OF THE AXIS BETWEEN 38W-44W...AND 150 NM N OF THE AXIS BETWEEN
45W-55W.

...DISCUSSION...

GULF OF MEXICO...
A WEAK SURFACE RIDGE IS ACROSS THE GULF OF MEXICO ANCHORED BY A
1018 MB HIGH NEAR 27N89W. A SURFACE TROUGH LINES THE MEXICO
COAST EXTENDING FROM 17N93W TO 24N96W. SURFACE CONVERGENCE NEAR
THE TROUGH ALONG WITH UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER
LEVEL HIGH OVER CENTRAL MEXICO NEAR 24N104W AND AN UPPER LEVEL
LOW OVER THE YUCATAN PENINSULA NEAR 19N89W ARE SUPPORTING
SCATTERED SHOWERS/THUNDERSTORMS ALONG THE WRN GULF FROM 21N-26N
W OF 92W. SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO ACROSS THE
NRN GULF N OF 28N BETWEEN 84W-96W. THIS ACTIVITY IS SUPPORTED BY
SURFACE CONVERGENCE AHEAD OF A COLD FRONT N OF THE AREA
EXTENDING ACROSS NW MISSISSIPPI...N LOUISIANA...AND INTO TEXAS.
THIS ACTIVITY IS ALSO ENHANCED BY UPPER LEVEL DIFFLUENCE
BETWEEN A LARGE UPPER LEVEL TROUGH ACROSS THE CENTRAL UNITED
STATES AND A SHORTWAVE RIDGE ACROSS THE NRN GULF EXTENDING FROM
THE NE FLORIDA PANHANDLE TO THE SRN TIP OF TEXAS. UPPER LEVEL
DIFFLUENCE BETWEEN THIS SHORTWAVE RIDGE AND AN UPPER LEVEL LOW N
OF THE BAHAMAS NEAR 29N77W IS SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS ACROSS THE FLORIDA PENINSULA N OF 24N E OF
83W. THE REMAINDER OF THE SRN AND CENTRAL GULF OF MEXICO IS
EXPERIENCING GENERALLY FAIR WEATHER UNDER THE INFLUENCE OF THE
SURFACE RIDGE...AND DRY AIR AND SUBSIDENCE ALOFT.

CARIBBEAN SEA...
UPPER LEVEL DIFFLUENCE TO THE E OF THE UPPER LEVEL LOW OVER THE
YUCATAN PENINSULA NEAR 19N89W IS FLARING UP ISOLATED
SHOWERS/THUNDERSTORMS IN THE W CARIBBEAN ESPECIALLY OVER
PORTIONS OF CUBA...JAMAICA...AND PARTS OF NRN CENTRAL AMERICA.
ISOLATED SHOWERS/POSSIBLE THUNDERSTORMS ARE ALSO ACROSS THE FAR
SW CARIBBEAN S OF 11N BETWEEN 72W-84W DUE TO SURFACE CONVERGENCE
NEAR A 1008 MB LOW OVER PANAMA NEAR 10N78W AND THE E PACIFIC
ITCZ WHICH STRETCHES ACROSS PANAMA TO THE LOW CENTER. A SURFACE
TROUGH EXTENDS ACROSS THE DOMINICAN REPUBLIC FROM 18N71W INTO
THE ATLC TO 24N70W. SURFACE CONVERGENCE NEAR THE TROUGH IS
GENERATING SHOWERS/THUNDERSTORMS ACROSS HISPANIOLA AND THE
ADJACENT WATERS. THE REMAINDER OF THE CARIBBEAN IS EXPERIENCING
GENERALLY FAIR WEATHER DUE TO DRY AIR AND SUBSIDENCE
ALOFT...EXCEPT FOR A FEW SHOWERS ACROSS THE WINDWARD ISLANDS DUE
TO AN APPROACHING TROPICAL WAVE CURRENTLY ALONG 57W. MODERATE
TRADEWINDS ARE ACROSS MUCH OF THE BASIN WITH STRONGER WINDS NEAR
THE COAST OF COLOMBIA. EXPECT THE TROPICAL WAVE ALONG 57W TO
REACH THE LESSER ANTILLES TOMORROW.

ATLANTIC OCEAN...
HURRICANE BILL REMAINS THE MAIN FEATURE ACROSS THE ATLC. SEE
SPECIAL FEATURES FOR DETAILS. SCATTERED SHOWERS/THUNDERSTORMS
ARE ACROSS THE FLORIDA PENINSULA N OF 24N W OF 80W DUE TO UPPER
LEVEL DIFFLUENCE BETWEEN A SHORTWAVE RIDGE ACROSS THE NRN GULF
AND AN UPPER LEVEL LOW N OF THE BAHAMAS NEAR 29N77W. A SURFACE
TROUGH EXTENDS ACROSS HISPANIOLA FROM 18N71W INTO THE ATLC TO
24N70W. A FEW ISOLATED SHOWERS/THUNDERSTORMS ARE NOTED ON THE N
SIDE OF THE ISLAND. THE REMAINDER OF THE ATLC OCEAN IS UNDER A
BROAD RIDGE ANCHORED BY A 1025 MB HIGH NEAR 35N51W AND A 1029 MB
AZORES HIGH NEAR 38N22W. BILL CONTINUES TO MOVE AROUND THE WRN
PERIPHERY OF THIS SFC RIDGE...BUT WILL SOON BECOME STEERED
NORTHWARD AND NORTHEASTWARD BY THE FLOW BETWEEN THE AZORES HIGH
AND A LARGE MID-LATITUDE TROUGH MOVING OVER THE EASTERN UNITED
STATES. AN UPPER LEVEL RIDGE DOMINATES THE ATLC BETWEEN 45W-75W
AS A RESULT OF THE OUTFLOW OF BILL. UPPER LEVEL DIFFLUENCE
BETWEEN THIS UPPER RIDGE AND AN UPPER LEVEL HIGH CENTERED NEAR
19N37W IS ENHANCING CONVECTION ALONG THE W PORTION OF THE ITCZ.

$$
WALTON


This weather bulletin was brought to you by:
www.nashvilleweather.net