[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 041759
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU SEP 04 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...

AT 04/1800 UTC...TROPICAL STORM HANNA IS CENTERED NEAR 25.1N
74.2W OR ABOUT 180 NM EAST OF NASSAU AND ABOUT 580 NM
SOUTH-SOUTHEAST OF WILMINGTON NORTH CAROLINA MOVING NW AT 12 KT.
THIS MOTION IS EXPECTED TO CONTINUE DURING THE NEXT DAY OR SO
WITH A GRADUAL INCREASE IN FORWARD SPEED. A TURN TO THE NORTH IS
EXPECTED BY LATE FRIDAY. THE CENTER OF HANNA WILL PASS JUST EAST
OF THE CENTRAL AND NORTHWESTERN BAHAMAS TODAY...AND WILL BE NEAR
THE SOUTHEAST COAST OF THE UNITED STATES BY LATE FRIDAY.
HOWEVER...RAINS AND WINDS ASSOCIATED WITH HANNA WILL REACH THE
COAST WELL IN ADVANCE OF THE CENTER. ESTIMATED MINIMUM CENTRAL
PRESSURE IS 989 MB. MAXIMUM SUSTAINED WIND SPEED IS 55 KT WITH
GUSTS TO 65 KT. LITTLE CHANGE IN STRENGTH IS FORECAST
TODAY...HOWEVER...HANNA COULD BECOME A HURRICANE ON FRIDAY PRIOR
TO REACHING THE COASTLINE. SEE LATEST NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC FOR MORE DETAILS.
CONVECTION ASSOCIATED WITH HANNA HAS DIMINISHED SUBSTANTIALLY
OVER THE PAST 6-12 HOURS. VERY DRY AIR ASSOCIATED WITH AN
UPPER-LEVEL LOW OVER CENTRAL CUBA IS CHOKING OFF CONVECTION NEAR
THE CORE OF HANNA... AND THE CYCLONE HAS A VERY SUBTROPICAL
APPEARANCE. HANNA COULD PRODUCE RAINFALL TOTALS OF 2 TO 4 INCHES
OVER THE NORTHERN BAHAMAS. SWELLS FROM HANNA ARE EXPECTED TO
INCREASE THE RISK OF DANGEROUS RIP CURRENTS ALONG PORTIONS OF
THE SOUTHEASTERN UNITED STATES COAST DURING THE NEXT COUPLE OF
DAYS.

AT 04/1500 UTC...HURRICANE IKE IS CENTERED NEAR 23.2N 57.0W OR
ABOUT 455 NM...845 KM...NORTHEAST OF THE LEEWARD ISLANDS MOVING
W-NW AT 14 KT. A GRADUAL TURN TOWARD THE WEST AND WEST-SOUTHWEST
IS EXPECTED OVER THE NEXT 48 HOURS AS A HIGH BUILDS IN TO THE
NORTHWEST OF IKE. THE HURRICANE WILL CONTINUE TO MOVE OVER THE
OPEN WATERS OF THE WEST-CENTRAL ATLANTIC DURING THE NEXT COUPLE
OF DAYS. IT IS TOO EARLY TO DETERMINE WHAT LAND AREAS MIGHT
EVENTUALLY BE AFFECTED BY IKE BUT INTERESTS IN THE SOUTHEASTERN
BAHAMAS AND THE TURKS AND CAICOS ISLANDS SHOULD MONITOR THE
PROGRESS OF THIS SYSTEM. ESTIMATED MINIMUM CENTRAL PRESSURE IS
938 MB. MAXIMUM SUSTAINED WIND SPEED IS 120 KT WITH GUSTS TO 145
KT. IKE IS A EXTREMELY DANGEROUS CATEGORY FOUR HURRICANE ON THE
SAFFIR-SIMPSON HURRICANE SCALE. SOME WEAKENING IS FORECAST
DURING THE NEXT DAY OR SO BUT IKE IS EXPECTED TO REMAIN A
POWERFUL HURRICANE FOR THE NEXT SEVERAL DAYS. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/ WMO HEADERS MIATCMAT4/WTNT24 KNHC
FOR MORE DETAILS. IKE CONTINUES TO DISPLAY A WELL-DEFINED EYE
WITH VERY COLD CLOUD TEMPERATURES IN THE EYEWALL. HOWEVER THE
CLOUD PATTERN IS NOW ASYMMETRIC DUE TO SOME NORTHERLY SHEAR
AFFECTING THE CYCLONE.

AT 04/1500 UTC...TROPICAL STORM JOSEPHINE IS CENTERED NEAR 14.5N
32.2W OR ABOUT 450 NM...840 KM...WEST OF THE SOUTHERNMOST CAPE
VERDE ISLANDS MOVING W-NW AT 9 KT...AND THIS MOTION IS EXPECTED
TO CONTINUE FOR THE NEXT COUPLE OF DAYS. ESTIMATED MINIMUM
CENTRAL PRESSURE IS 1000 MB. MAXIMUM SUSTAINED WIND SPEED IS 45
KT WITH GUSTS TO 55 KT. UPPER-LEVEL WINDS ARE CURRENTLY NOT
FAVORABLE FOR SIGNIFICANT STRENGTHENING...AND LITTLE CHANGE IN
STRENGTH IS FORECAST DURING THE NEXT COUPLE OF DAYS.SEE LATEST
NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT5/WTNT25
KNHC FOR MORE DETAILS. THE DEEP CONVECTION THAT WAS PRESENT
EARLY THIS MORNING HAS DISSIPATED...LEAVING AN EXPOSED LOW-LEVEL
CENTER WELL TO THE SOUTHWEST OF SMALL AREAS OF DISORGANIZED
CONVECTION.

...TROPICAL WAVES...

A TROPICAL WAVE HAS ALREADY PUSHED WEST OF DAKAR PER RECENT
OBSERVED SOUNDING. THE WAVE AXIS IS CENTERED ALONG 18W S OF
18N...MOVING W NEAR 10 KT. SATELLITE IMAGERY DEPICTS MODERATE
CURVATURE IN THE SURFACE WIND FIELD AROUND 12N. HOWEVER...MOST
OF THE SHOWER ACTIVITY IS ACROSS THE NORTHERN END OF THE
WAVE...COVERING THE AREA FROM 15N TO 20N EAST OF 22 W TO THE
AFRICAN COAST. THE LEADING EDGE OF THE SHOWER ACTIVITY HAS
REACHED THE EASTERNMOST CAPE VERDE ISLANDS.

A NEW LOW AMPLITUDE TROPICAL WAVE HAS BEEN ADDED ON THE 12Z
SURFACE MAP BASED SATELLITE IMAGERY AND TPW PRODUCT FROM CIMMS.
THE WAVE AXIS IS ALONG 43W S OF 16N...MOVING W 10 TO 15 KT. THIS
TROPICAL WAVE IS PRODUCING A LARGE AREA OF SCATTERED MODERATE
CONVECTION FROM 11N TO 16N BETWEEN 42W AND 50W...WITH THE
STRONGEST ACTIVITY WELL AHEAD OF THE WAVE AXIS. IN ADDITION...A
ASCAT PASS FROM AROUND 12Z ALSO SHOWED A WIND SHIFT IN
ASSOCIATION WITH THE WAVE AXIS.

...THE ITCZ...

THE ITCZ AXIS IS ANALYZED ALONG 9N14W 10N24W 8N37W 8N50W 10N62W.
ISOLATED MODERATE CONVECTION IS MAINLY SOUTH OF THE ITCZ AXIS
FROM 6N TO 9N BETWEEN 40W AND 51W.

...DISCUSSION...

GULF OF MEXICO...
THE EXTRATROPICAL REMNANT LOW ASSOCIATED WITH THE FORMER T.D.
GUSTAV IS CURRENTLY CENTERED OVER MISSOURI. RAINFALL TOTALS OF
UP TO 20 INCHES HAVE BEEN REPORTED IN LOUISIANA. A SURFACE
TROUGH TRAILS FROM THE LOW TO THE NORTHWEST GULF...EXTENDING
FROM SOUTHWEST LOUISIANA TO DEEP SOUTH TEXAS. A NARROW BAND OF
SHOWERS WITH EMBEDDED THUNDERSTORMS IS WITHIN 75 NM AHEAD OF THE
TROUGH....PARTICULARLY NORTH OF 27N. ANOTHER SURFACE TROUGH IS
LOCATED OVER THE BAY OF CAMPECHE...RESULTING IN SCATTERED
SHOWERS AND THUNDERSTORMS SOUTH OF 20N...NEAR MINATITLAN MEXICO.
A WEAK SURFACE RIDGE EXTENDING FROM THE SOUTHEAST CONUS TO THE
EASTERN GULF SEPARATES THE SURFACE TROUGHS OVER THE WESTERN GULF
FROM THE LARGE CIRCULATION ASSOCIATED WITH TROPICAL STORM HANNA.
AN UPPER LEVEL HIGH OVER SOUTHERN BAJA PENINSULA AND ITS
ASSOCIATED RIDGE ARE IMPACTING MUCH OF THE GULF. A STRONG UPPER
LEVEL LOW CENTERED OVER CENTRAL CUBA IS PRODUCING DRY NORTHERLY
UPPER LEVEL FLOW OVER THE FAR EASTERN GULF.

CARIBBEAN SEA...
AN UPPER LEVEL RIDGE EXTENDING SOUTHWESTWARD FROM AN UPPER LEVEL
HIGH OVER THE WEST CENTRAL ATLANTIC...COMBINED WITH THE
AFOREMENTIONED UPPER LEVEL LOW OVER CUBA...IS RESULTING IN A
LARGE AREA OF SCATTERED MODERATE CONVECTION OVER THE CENTRAL
CARIBBEAN. SOME SHOWER AND THUNDERSTORM ACTIVITY IS IMPACTING
HISPANIOLA...THE ABC ISLANDS AND WESTERN VENEZUELA...INCLUDING
THE LAKE MARACAIBO AREA. THE SAN JUAN DOPPLER RADAR ALSO SHOWS A
LINE OF SHOWERS AND TSTMS AFFECTING THE WESTERN PORTION OF THE
ISLANDS. DUE TO THE RECENT HEAVY RAINFALL ACROSS THE ISLANDS
ASSOCIATED WITH HANNA'S CIRCULATION...THE TERRAINS REMAINS
SATURATED...AND ANY ADDITIONAL RAIN WILL CAUSE LOCALIZED
FLOODING OF RIVERS...SMALL STREAMS AND CREEKS. AS A RESULT...A
FLASH FLOOD WATCH WILL REMAIN IN EFFECT UNTIL 4 PM AST THIS
AFTERNOON. ST THOMAS VI REPORTED 1.35 INCHES OF RAIN IN 24 HOURS
THROUGH THIS MORNING. LOW LEVEL CONVERGENCE ALONG THE WEST COAST
OF CENTRAL AMERICA IS GENERATING A LARGE AREA OF CLOUDINESS WITH
EMBEDDED SHOWERS. DRY EASTERLY UPPER LEVEL FLOW COMBINED WITH
MODERATE SUBSIDENCE IS LIMITED CONVECTIVE ACTIVITY OVER THE FAR
EASTERN CARIBBEAN. UNUSUAL SOUTHWESTERLY SURFACE WINDS IN
ASSOCIATION WITH THE LARGE CIRCULATION OF HANNA CONTINUE
IMPACTING THE CENTRAL CARIBBEAN.

ATLANTIC OCEAN...
CONSISTENT WITH CLIMATOLOGY...THREE TROPICAL CYCLONES ARE
LOCATED IN THE DISCUSSION AREA...SEE SPECIAL FEATURES ABOVE FOR
DETAILS. FROM EAST TO WEST...THE THREE ARE...TROPICAL STORM
JOSEPHINE...HURRICANE IKE...AND TROPICAL STORM HANNA. THE
PREVIOUSLY MENTIONED UPPER LEVEL HIGH OVER THE WEST CENTRAL
ATLANTIC IS CENTERED NEAR 28N63W. AN UPPER LEVEL LOW IS
CENTERED NEAR 19N41W. MODERATE NORTHERLY UPPER LEVEL FLOW
CONTINUES OVER THE CENTRAL ATLANTIC NORTH OF 20N. THE REMAINDER
OF THE FORECAST AREA IS DOMINATED BY AN UPPER LEVEL RIDGE OVER
THE WESTERN COAST OF AFRICA NEAR 20N16W. AT THE SURFACE...A 1027
MB HIGH LOCATED NEAR 35N45W COVERS THE NORTHERN PORTION OF THE
EASTERN AND CENTRAL ATLANTIC. DURING THE NEXT 24 HOURS...THE
HIGH IS FORECAST TO MOVE WESTWARD.

$$
COHEN/RUBIO




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