[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 211802
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...SPECIAL FEATURES...
AS OF 1800 UTC...HURRICANE BILL IS CENTERED NEAR 28.5N 66.8W
ABOUT 255 NM...465 KM...SOUTH-SOUTHWEST OF BERMUDA AND ABOUT
6O5 NM...1115 KM...SOUTHEAST OF CAPE HATTERAS NORTH CAROLINA.
MOVING NW OR 325 DEG AT 16 KT. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 957 MB. MAXIMUM SUSTAINED WIND SPEEDS ARE 100 KT
WITH GUSTS TO 120 KT. BILL IS A CATEGORY THREE HURRICANE ON THE
SAFFIR-SIMPSON SCALE. SOME FLUCTUATIONS IN INTENSITY ARE LIKELY
THE REST OF TODAY AND SATURDAY. A TROPICAL STORM WARNING AND A
HURRICANE WATCH ARE IN EFFECT FOR BERMUDA. RADAR IMAGERY FROM
BERMUDA INDICATES THAT SOME RAINBANDS ARE ALREADY AFFECTING THE
ISLAND. SEE THE LATEST FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
TCMAT3/WTNT23 KNHC FOR MORE DETAILS. NUMEROUS STRONG CONVECTION
IS WITHIN 80 NM OF CENTER OF BILL. LARGE SWELLS GENERATED BY
THIS HURRICANE ARE AFFECTING PUERTO RICO...HISPANIOLA...THE
BAHAMAS...AND BERMUDA...AND SHOULD BEGIN AFFECTING MOST 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. THE
METEOROLOGICAL SERVICE OF THE DOMINICAN REPUBLIC REPORTED SOME
COASTAL FLOODING WITH DAMAGE TO ROADS AND HOUSES DUE TO HIGH
WAVES ALONG THE NORTH COAST OF THE ISLAND.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 28W/29W S OF 17N MOVING W NEAR 15 KT.
THE WAVE COINCIDES WITH A DEEP LAYERED MOISTURE MAXIMUM OBSERVED
IN THE TOTAL PRECIPITABLE WATER IMAGERY. AN INCREASE IN MODERATE
CONVECTION IS NOTED JUST AHEAD OF THE WAVE AXIS WITH SOME
CYCLONIC TURNING NEAR 12N. THIS IS CONFIRMED BY ASCAT DATA FROM
AROUND 1100 UTC AND VIS SATELLITE IMAGERY. SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS FROM 11N-14N BETWEEN
29W-33W.

A TROPICAL WAVE IS ALONG 56W S OF 16N MOVING W NEAR 20 KT.
CONVECTION HAS ALSO INCREASED EITHER SIDE OF THE WAVE AXIS
PARTICULARLY S OF 12N. THIS WAVE LIES WITHIN A BROAD AREA OF
DEEP LAYER MOISTURE OBSERVED IN TOTAL PRECIPITABLE WATER
IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS NOTED
FROM 8N-12N BETWEEN 52W-57W.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 13N17W 10N35W 10N50W 9N61W. A
CLUSTER OF NUMEROUS MODERATE/ISOLATED STRONG CONVECTION HAS
MOVED OFF THE AFRICA COAST FROM 10N-13N BETWEEN 18W-21W. THIS
CONVECTIVE ACTIVITY IS MOST LIKELY ASSOCIATED WITH NEXT TROPICAL
WAVE. IN ADDITION TO CONVECTION ASSOCIATED WITH THE TROPICAL
WAVES...SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
7N-11N BETWEEN 36W-52W.

...DISCUSSION...

GULF OF MEXICO...
A WEAK SURFACE RIDGE IS ACROSS THE GULF OF MEXICO BUILDING FROM
THE W ATLC WITH A 1019 MB HIGH NEAR 29N88W AT 1500 UTC. A WEAK
SFC TROUGH HAS DEVELOPED OVER THE SW PORTION OF THE AREA
GENERATING SOME SHOWER AND TSTM ACTIVITY. A QSCAT PASS SHOWS SE
WINDS OF 15 TO 20 KT BEHIND THE TROUGH AXIS WHILE NOAA BUOY
42005 IN THE SW GULF IS REPORTING SUSTAINED WINDS OF 21 KT.
SCATTERED SHOWERS AND TSTMS ARE ALSO NOTED OVER THE REGION N OF
27N E OF 93W. A DIFFLUENT PATTERN ALOFT...AHEAD OF A DEEP LAYER
TROUGH DIGGING S OVER THE E CONUS AND THE NORTHERN GULF
WATERS...IS ENHANCING THIS ACTIVITY. AN UPPER LEVEL RIDGE COVERS
MOST OF THE GULF EXTENDING FROM AN UPPER LEVEL HIGH CENTER OVER
MEXICO NEAR 23N104W. THE UPPER-LEVEL LOW THAT WAS MOVING IN
TANDEM WITH THE REMNANTS OF ANA A FEW DAYS AGO IS NOW CENTERED
OVER NORTHERN BELIZE. IT IS INDUCING SCATTERED SHOWERS AND
TSTMS OVER THE NW CARIBBEAN. THE SE GULF IS EXPERIENCING
GENERALLY FAIR WEATHER UNDER THE INFLUENCE OF DRY AIR AND
SUBSIDENCE ALOFT. LOOKING AHEAD...THE RIDGE ACROSS THE N GULF IS
FORECAST TO MOVE S TO ALONG 25N BY SAT. A WEAK FRONTAL TROUGH IS
EXPECTED TO EXTEND ACROSS THE GULF N OF 27N DURING THE UPCOMING
WEEKEND.

CARIBBEAN SEA...
AS PREVIOUSLY MENTIONED...AN UPPER-LEVEL LOW IS GENERATING
SCATTERED SHOWERS AND TSTMS OVER THE NW CARIBBEAN...INCLUDING
THE GULF OF HONDURAS. SIMILAR CONVECTIVE ACTIVITY IS ALSO NOTED
OVER THE SW CARIBBEAN S OF 12N AND OVER PARTS OF PANAMA AND
COSTA RICA. THIS ACTIVITY IS ASSOCIATED WITH THE COLOMBIAN OR
PANAMANIAN LOW...ANALYZED 1008 MB NEAR 10N77W. LOW-TOPPED TRADE
WIND SHOWERS DOT THE REMAINDER OF THE AREA UNDER DRY SUBSIDENCE
AIR ALOFT. MOISTURE ASSOCIATED WITH THE TROPICAL WAVE ALONG 56W
IS ALREADY REACHING THE WINDWARD ISLANDS WITH BARBADOS REPORTING
A FEW PASSING LIGHT SHOWERS. NARROW LINES OF SHOWERS ARE ACROSS
THE FAR NE ISLANDS AS WELL AS ACROSS THE LESSER ANTILLES
ASSOCIATED WITH THE LARGE CYCLONIC FLOW AROUND HURRICANE BILL.
MODERATE TRADE WINDS ARE BLOWING ACROSS MUCH OF THE BASIN WITH
STRONGER WINDS NEAR THE COAST OF COLOMBIA WHERE A QSCAT PASS
FROM THIS MORNING SHOWED NE WINDS OF 20 KT.

ATLANTIC OCEAN...
HURRICANE BILL REMAINS THE MAIN FEATURE ACROSS THE ATLC. SEE
SPECIAL FEATURES FOR DETAILS. THE REMAINDER OF THE ATLC OCEAN IS
UNDER A BROAD RIDGE ANCHORED BY A 1030 MB AZORES HIGH NEAR
39N22W. BILL CONTINUES TO MOVE AROUND THE WESTERN 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 DEVELOPING OVER THE EASTERN UNITED STATES. A
WEAK UPPER-LEVEL LOW IS NE OF THE NW BAHAMAS NEAR 28N75W. AN
UPPER LEVEL ANTICYCLONE...EXISTING AS A RESULT OF THE OUTFLOW OF
HURRICANE BILL...IS CENTERED NEAR 24N56W. IT DOMINATES MOST OF
THE AREA BETWEEN 50W AND 70W. THE RIDGE EXTENDS INTO THE EASTERN
CARIBBEAN PRODUCING MOSTLY FAIR WEATHER OVER THE ABC ISLANDS.

$$
GR/JA





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