[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 202345
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
2245 UTC.

...SPECIAL FEATURES...
AS OF 2100 UTC...HURRICANE BILL IS CENTERED NEAR 23.8N 63.2W OR
ABOUT 595 MILES...960 KM...S OF BERMUDA AND ABOUT 1080
MILES...1735 KM...SE OF CAPE HATTERAS NORTH CAROLINA MOVING NW
OR 305 DEG AT 16 KT. THE LATEST MINIMUM CENTRAL PRESSURE IS 948
MB REPORTED BY AN AIR FORCE RECONNAISSANCE AIRCRAFT A FEW HOURS
AGO. MAXIMUM SUSTAINED WIND SPEEDS HAVE INCREASED TO 110 KT WITH
GUSTS UP TO 135 KT. HURRICANE FORCE WINDS EXTEND OUTWARD UP TO
115 MILES...185 KM...FROM THE CENTER...AND TROPICAL STORM FORCE
WINDS EXTEND OUTWARD UP TO 260 MILES...415 KM. A TROPICAL STORM
WARNING AND A HURRICANE WATCH HAVE BEEN ISSUED FOR BERMUDA. SEE
THE LATEST FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
TCMAT3/WTNT23 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION
IS NEAR THE CENTER OF THE HURRICANE FROM 22N-25N BETWEEN
61W-64W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS
OBSERVED IN THE OUTER RAINBANDS ESPECIALLY TO THE NE OF THE
CENTER. LARGE SWELLS GENERATED BY BILL ARE AFFECTING THE
NORTHERN LEEWARD ISLANDS...PUERTO RICO AND HISPANIOLA...AND
SHOULD BEGIN AFFECTING THE BAHAMAS...BERMUDA...MOST OF THE U.S.
EAST COAST...AND THE ATLANTIC MARITIMES OF CANADA DURING THE
NEXT FEW DAYS. THESE SWELLS WILL LIKELY CAUSE EXTREMELY
DANGEROUS SURF AND LIFE-THREATENING RIP CURRENTS.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 24W S OF 17N ACROSS THE CAPE VERDE
ISLANDS MOVING W NEAR 10 KT. THE WAVE COINCIDES WITH A DEEP
LAYERED MOISTURE MAXIMUM OBSERVED IN THE TOTAL PRECIPITABLE
WATER IMAGERY. AN INVERTED-V LOW LEVEL SIGNATURE IS NOTED ON
RECENT SATELLITE PICTURES WITH SOME CYCLONIC TURNING NEAR THE
INTERSECTION OF THE WAVE WITH THE ITCZ. THIS IS CONFIRMED BY AN
ASCAT SCATTEROMETER PASS FROM EARLIER TODAY. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 12N-14N BETWEEN
25W-28W.

A TROPICAL WAVE EXTENDS FROM 17N52W TO 7N49W MOVING W NEAR 20
KT. THIS WAVE LIES WITHIN A BROAD AREA OF DEEP LAYER MOISTURE
OBSERVED IN TOTAL PRECIPITABLE WATER IMAGERY. NO DEEP CONVECTION
IS CURRENTLY ASSOCIATED WITH THE WAVE.

A TROPICAL WAVE IS ACROSS THE YUCATAN PENINSULA ALONG 90W S OF
21N MOVING W NEAR 15 KT. THIS WAVE LIES WITHIN A BROAD DEEP
LAYER MOISTURE MAXIMUM IN THE E PACIFIC OBSERVED IN TOTAL
PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS FROM 14N-20N BETWEEN 89W-94W. THIS ACTIVITY IS
ENHANCED BY UPPER LEVEL DIFFLUENCE.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 13N13W 12N26W 9N33W 10N44W 8N55W
10N61W. A CLUSTER OF NUMEROUS MODERATE/SCATTERED STRONG
CONVECTION IS JUST OFF THE AFRICA COAST FROM 11N-14N BETWEEN
16W-18W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
9N-11N BETWEEN 20W-22W. SIMILAR ACTIVITY IS FROM 7N-10N BETWEEN
28W-24W.

...DISCUSSION...

GULF OF MEXICO...
A WEAK SURFACE RIDGE IS ACROSS THE GULF OF MEXICO BUILDING FROM
THE W ATLC. AN UPPER LEVEL RIDGE COVERS MOST OF THE GULF
EXTENDING FROM ONE UPPER LEVEL HIGH CENTER E OF N CAROLINA NEAR
35N75W TO A SECOND UPPER LEVEL HIGH CENTERED OVER MEXICO NEAR
21N101W. AN OUTFLOW BOUNDARY N OF THE DISCUSSION AREA ACROSS
MISSISSIPPI AND SRN ARKANSAS...AS WELL AS UPPER LEVEL
DIFFLUENCE BETWEEN THE UPPER RIDGE AND AN UPPER LEVEL TROUGH
OVER THE N CENTRAL UNITED STATES ARE SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS ACROSS THE NRN GULF N OF 27 E OF 95W.
UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER RIDGE AND AN UPPER
LEVEL LOW OVER BELIZE NEAR 18N88W IS SUPPORTING
SHOWERS/THUNDERSTORMS IN THE ERN BAY OF CAMPECHE FROM 18N-20N
BETWEEN 90W-92W. THIS ACTIVITY MAY BE ENHANCED BY THE TROPICAL
WAVE ALONG 90W. THE REMAINDER OF THE SE GULF IS EXPERIENCING
GENERALLY FAIR WEATHER UNDER THE INFLUENCE OF DRY AIR AND
SUBSIDENCE ALOFT. EXPECT SHOWERS/THUNDERSTORMS TO REMAIN ACROSS
THE SW GULF IN THE BAY OF CAMPECHE AS THE TROPICAL WAVE OVER THE
YUCATAN MOVES WWD.

CARIBBEAN SEA...
A FEW ISOLATED SHOWERS ARE IN THE NW CARIBBEAN N OF HONDURAS DUE
TO UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LEVEL LOW OVER
BELIZE NEAR 18N88W AND AN UPPER LEVEL RIDGE OVER THE SW
CARIBBEAN. SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS THE SW
CARIBBEAN S OF 11N BETWEEN 75W-85W AFFECTING PANAMA AND COSTA
RICA. THESE SHOWERS ARE GENERATED BY SURFACE CONVERGENCE NEAR
THE E PACIFIC ITCZ AND A 1007 MB SURFACE LOW ALONG THE COAST OF
COLUMBIA NEAR 10N76W. NARROW LINES OF SHOWERS ARE ACROSS THE FAR
NE ISLANDS AS WELL AS ACROSS THE LESSER ANTILLES ASSOCIATED WITH
CYCLONIC FLOW AROUND HURRICANE BILL. THE REMAINDER OF THE
CARIBBEAN IS UNDER DRY SUBSIDENCE AIR ALOFT SUPPORTING GENERALLY
FAIR WEATHER. MODERATE TRADEWINDS ARE ACROSS MUCH OF THE BASIN
WITH STRONGER WINDS NEAR THE COAST OF COLUMBIA.

ATLANTIC OCEAN...
HURRICANE BILL REMAINS THE DOMINANT FEATURE ACROSS THE ATLC. SEE
SPECIAL FEATURES FOR DETAILS. THE REMAINDER OF THE ATLC IS UNDER
A BROAD RIDGE ANCHORED BY A 1029 MB AZORES HIGH NEAR 40N23W.
BILL CONTINUES TO MOVE AROUND THE PERIPHERY OF THIS SFC RIDGE.
IN THE UPPER LEVELS...A NARROW UPPER TROUGH IS E OF THE BAHAMAS
WITH AXIS ALONG 73W. AN UPPER LEVEL RIDGE IS E OF THE STRONG
OUTFLOW OF BILL CENTERED NEAR 24N53W. ANOTHER UPPER LEVEL HIGH
DOMINATES THE E ATLC CENTERED NEAR 30N33W.

$$
WALTON






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