[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 110009
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU JUL 10 2008

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 FEATURE....

THE CENTER OF HURRICANE BERTHA AT 10/2100 UTC IS NEAR 27.2N
60.8W. BERTHA IS MOVING NORTHWEST OR 315 DEGREES AT 9 KT. THE
ESTIMATED MINIMUM CENTRAL PRESSURE IS 980 MB. THE MAXIMUM
SUSTAINED WIND SPEEDS ARE NOW 75 KT WITH GUSTS TO 90 KT MAKING
BERTHA A CATEGORY 1 HURRICANE ON THE SAFFIR-SIMPSON SCALE.
BERTHA IS LOCATED ABOUT 425 MILES...685 KM...SOUTHEAST OF
BERMUDA. LONG PERIOD SWELLS OF 12-13 SECONDS ASSOCIATED WITH
BERTHA ARE NOW AFFECTING BERMUDA. SATELLITE IMAGERY INDICATES
THAT THE EYE OF BERTHA HAS BECOME BETTER DEFINED THIS AFTERNOON.
HOWEVER...CONVECTIVE TOPS IN THE EYEWALL HAVE WARMED AND THERE
ARE SIGNS THAT THE SYSTEM MAY BE ENTRAINING SOME DRY AIR. THE
INITIAL INTENSITY HAS THUS BEEN REDUCED TO 75 KT. NONETHELESS
THE ATMOSPHERE IS EXPECTED TO REMAIN FAVORABLE FOR ADDITIONAL
STRENGTHENING AS A LARGE UPPER-LEVEL ANTICYCLONE DEVELOPS OVER
BERTHA DURING THE NEXT 24-48 HOURS. IN ADDITION...THE SYSTEM IS
STILL OVER WARM WATER. GIVEN THE ENVIRONMENT...THE INTENSITY
FORECAST CALLS FOR MODEST STRENGTHENING IN 24 HOURS. LATER IN
THE FORECAST PERIOD...BERTHA IS EXPECTED TO MOVE OUT FROM UNDER
THE ANTICYCLONE AND ENCOUNTER VERTICAL WIND SHEAR.  THIS SHOULD
OCCUR AS BERTHA REACHES COOLER WATERS AND RESULT IN A WEAKENING
TREND. DUE TO THE UNCERTAINTY IN THE FORECAST TRACK...INTERESTS
IN BERMUDA SHOULD CLOSELY MONITOR THE PROGRESS OF BERTHA DURING
THE NEXT SEVERAL DAYS. PLEASE REFER TO THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
AND THE PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE
DETAILS.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 36W SOUTH OF 13N IS MOVING WEST 10 TO
15 KT. INVERTED-V PATTERN SEEN EARLIER ON VIS SAT IMAGERY IS
ALSO NOTED IN IR IMAGERY AS WELL. POCKETS OF MODERATE CONVECTION
ARE NOTED NEAR THE INTERSECTION OF THE WAVE AXIS AND THE ITCZ.
LOW-LEVEL SATELLITE DERIVED WINDS ALSO SUPPORT THE POSITION OF
THE WAVE AXIS.

A TROPICAL WAVE IS ALONG 61W/62W SOUTH OF 14N IS MOVING WEST AT
15 KT. MOST OF THE CONVECTION ASSOCIATED WITH THE WAVE HAS MOVED
INTO THE EASTERN CARIBBEAN SEA. HOWEVER SOME ACTIVITY CONTINUES
OVER PORTIONS OF TRINIDAD AND GRENADA. SCATTERED MODERATE TO
ISOLATED STRONG CONVECTION IS FROM 11N TO 14N BETWEEN 63W AND
70W. A DIFFLUENT PATTERN ALOFT IS HELPING TO INDUCE THIS SHOWER
AND TSTM ACTIVITY.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 11N15W 8N22W 8N30W 5N42W 8N59W.
SCATTERED MODERATE CONVECTION IS FROM 4N TO 9N BETWEEN 25W AND
30W. SIMILAR CONVECTION IS FROM 9N TO 11N BETWEEN 40W AND 45W
AND NEAR 7N51W. A CLUSTER OF SCATTERED MODERATE ISOLATED  STRONG
CONVECTION HAS MOVED OFFSHORE OF SENEGAL AND GUINEA BISSAU.
THIS CONVECTION IS OCCURRING IN ADVANCE OF THE NEXT TROPICAL
WAVE JUST ABOUT TO EMERGE OFF THE AFRICAN COAST.

...DISCUSSION...

THE GULF OF MEXICO...
MIDDLE TO UPPER-LEVEL RIDGE CENTERED OVER THE SE CONUS COVERS
MOST OF THE GULF REGION WHILE A WEAK CYCLONIC CIRCULATION
REMAINS OVER THE BAY OF CAMPECHE. A SFC TROUGH ALONG 24N97W TO
19N95W IS DRIFTING WESTWARD. SCATTERED SHOWERS AND ISOLATED
TSTMS ASSOCIATED WITH THIS FEATURE OVER THE BAY OF CAMPECHE
HAVE WEAKENED. HOWEVER A CLUSTER OF STRONG THUNDERSTORMS ARE
SLIDING ACROSS THE EXTREME SOUTHERN BAY OF CAMPECHE AFTER
EMERGING OFF THE ISTHMUS OF TEHUANTEPEC. ISOLATED SHOWERS OR
THUNDERSTORMS ARE NOTED OVER THE REMAINDER OF THE GULF THANKS TO
THE INFLUENCE OF THE RIDGE. AT THE SURFACE...A WEAK RIDGE OF
HIGH PRESSURE DOMINATES THE GULF GIVING THE AREA MAINLY LIGHT TO
MODERATE WINDS. THE STRONGEST WINDS UP TO 20 KT ARE FOUND OVER
THE BAY CAMPECHE DUE A SLIGHTLY THIGH PRES GRADIENT BETWEEN THE
RIDGE AND THE SFC TROUGH.

THE CARIBBEAN SEA...
A MIDDLE TO UPPER-LEVEL TROUGH FROM THE W ATLC EXTENDS SW ACROSS
EASTERN CUBA AND THE NORTHWEST CARIBBEAN SEA GENERATING
SCATTERED SHOWERS AND TSTMS. AN UPPER-LEVEL RIDGE ANCHORED ON A
HIGH OVER NORTHERN COLOMBIA IS SOUTH OF THIS TROUGH. UPPER
DIFFLUENT FLOW ASSOCIATED WITH THIS FEATURE IS ENHANCING
SCATTERED MODERATE CONVECTION OVER THE SW CARIBBEAN. AS
PREVIOUSLY MENTIONED A TROPICAL WAVE IS AFFECTING THE WINDWARD
ISLANDS AND THE FAR SE CARIBBEAN SEA. SEE TROPICAL WAVE SECTION
FOR DETAILS. NARROW BANDS OF MAINLY LOW CLOUDS ASSOCIATED WITH
THE PERIPHERAL CIRCULATION OF HURRICANE BERTHA ARE MOVING ACROSS
THE NORTHEAST LEEWARD ISLANDS...THE UK/US VIRGIN ISLANDS AND
PUERTO RICO. MODERATE TRADE WINDS ARE BLOWING ACROSS THE BASIN.
THESE WINDS ARE FORECAST TO INCREASE UP TO 30 KT NEAR THE
COLOMBIAN COAST BEGINNING TONIGHT THROUGH AT LEAST SUN MORNING
AS PRES GRADIENT TIGHTENS OVER THE E AND CENTRAL CARIBBEAN.

THE ATLANTIC OCEAN...
A STATIONARY MIDDLE TO UPPER LEVEL CYCLONIC CIRCULATION CENTER
IS NEAR 28N70W. CYCLONIC FLOW AROUND THIS CENTER EXTENDS SW
ACROSS THE BAHAMAS AND EASTERN CUBA. A MIDDLE TO UPPER LEVEL
TROUGH IS DROPPING SOUTHWARD JUST TO THE NORTHEAST OF HURRICANE
BERTHA...WITH AXIS CLIPPING THE FORECAST AREA NEAR 29N48W. THIS
TROUGH SUPPORTS A COLD FRONT LOCATED OVER THE CENTRAL ATLC.
OUTSIDE OF HURRICANE BERTHA...A SURFACE RIDGE DOMINATES THE
REMAINDER OF THE ATLC DISCUSSION AREA WITH A 1026 MB HIGH
CENTERED NEAR 32N31W. THIS SFC HIGH PAIRED WITH LOWER PRES OVER
WESTERN AFRICA IS PRODUCING A SWATH OF MODERATE TO STRONG NE
WINDS N OF 20N AND E OF 20W...INCLUDING THE CANARY ISLANDS. A
SHEARED MIDDLE TO UPPER LEVEL TROUGH ENTERS THE THE EASTERN
ATLANTIC NEAR 32N24W THEN CONTINUES SW TO NEAR 22N34W. MID TO
UPPER LEVEL RIDGE ANCHORED ON A HIGH OVER MAINLAND AFRICA
DOMINATES THE FLOW OVER THE DEEP TROPICS PARTICULARLY E OF 50W.

$$
COBB



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