[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 200554
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT TUE SEP 20 2005

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM
THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON
SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND
METEOROLOGICAL ANALYSIS.

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0315 UTC.

...SPECIAL FEATURES...

TROPICAL STORM RITA IS CENTERED NEAR 23.6N 78.8W...OR 175 NM ESE
OF KEY WEST FLORIDA...AT 20/0600 UTC MOVING WNW AT 15 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 991 MB. MAXIMUM SUSTAINED
WIND SPEED IS 60 KT WITH GUSTS TO 75 KT. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC
AND THE PUBLIC ADVISORY UNDER HEADERS MIATCPAT3/WTNT33 KNHC FOR
MORE DETAILS. RITA CONTINUES TO MAINTAIN STRONG CONVECTION
SURROUNDING THE LOW-LEVEL CENTER WITH SPIRAL BANDS BECOMING MORE
ESTABLISHED FROM OVER BAHAMA ISLANDS...CENTRAL CUBA AND MOVING
OVER S FLORIDA AND THE UPPER KEYS. AN OUTER RAINBAND EXTENDS AS
FAR N AS LAKE OKEECHOBEE. AN UPPER LOW LOCATED BETWEEN JAMAICA
AND THE CAYMAN ISLANDS IS LIMITING OUTFLOW TO THE S AND HAS
PERHAPS PLACED SLIGHT SE SHEAR OVER THE CENTER. NUMEROUS STRONG
CONVECTION IS WITHIN A 60 NM RADIUS OF 23N77W. SCATTERED
MODERATE/STRONG CONVECTION COVERS THE REMAINDER OF THE AREA FROM
21N-26.5N BETWEEN 74W-81.5W. DESPITE THE OUTFLOW PATTERN...RITA
IS EXPECTED TO STRENGTHEN TO HURRICANE STATUS TONIGHT OVER THE
WARM WATERS OF THE BAHAMA BANKS AND STILL HAS THE POTENTIAL TO
BE A MAJOR HURRICANE OVER THE SE GULF IN THE NEXT 1-2 DAYS.

HURRICANE PHILIPPE IS CENTERED NEAR 18.3N 56.8W...OR 295 NM E OF
THE LEEWARD ISLANDS...AT 20/0300 UTC MOVING NNW AT 5 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 985 MB. MAXIMUM SUSTAINED
WIND SPEED IS 70 KT WITH GUSTS TO 85 KT. SEE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
FOR MORE DETAILS. PHILIPPE CONVECTIVE STRUCTURE OVER THE PAST
SEVERAL HOURS HAS ELONGATED TOWARD THE NNE. AN UPPER LEVEL RIDGE
LIES E OF THE STORM AND IS CAUSING THE OUTFLOW TO GOOD IN ALL
BUT THE W QUADRANT. NUMEROUS STRONG CONVECTION IS WITHIN A 75 NM
RADIUS OF 18N56W. SCATTERED MODERATE/STRONG COVERS THE AREA FROM
16N-21N BETWEEN 53W-58W. CLUSTERS OF SCATTERED MODERATE/ISOLATED
STRONG CONVECTION ARE WITHIN 90/120 NM OF LINE FROM
13N58W-20N51W. SHOWERS/THUNDERSTORMS ARE CROSSING PARTS OF THE
LEEWARD ISLANDS BUT THE HEAVIEST CONVECTION IS EXPECTED TO
REMAIN WELL TO THE E AS PHILIPPE TRACKS N OVER THE NEXT SEVERAL
DAYS.

...TROPICAL WAVES...

E ATLC TROPICAL WAVE IS ALONG 26W/27W S OF 17N MOVING W 10 KT
WITH A WEAK 1014 MB LOW ALONG THE WAVE NEAR 10N. WELL-DEFINED
LOW-LEVEL CURVATURE IS SW OF THE CAPE VERDE ISLANDS. NO
ASSOCIATED DEEP CONVECTION.

CENTRAL ATLC TROPICAL WAVE IS ALONG 42W/43W S OF 18N MOVING W 10
KT. THE N PORTION OF THIS WAVE HAS SEPARATED AND IS NOW A
SURFACE TROUGH ALONG 26N43W TO A 1014 MB LOW NEAR 18N45W MOVING
W 15-20 KT. WAVE STILL HAS A WELL-DEFINED CURVATURE ON INFRARED
SATELLITE IMAGERY.

THE MAIN FOCUS IS NOW ON THE SURFACE TROUGH EXTENDING FROM
26N43W TO A 1014 MB LOW NEAR 18N45W. NUMEROUS STRONG CONVECTION
IS BEING DRAWN INTO THE LOW FROM THE TROPICAL WAVE TO THE E
WITHIN 45 NM OF LINE 16N41W-19N64W. THIS IS DUE TO THE UPPER
DIFFLUENCE FROM THE UPPER HIGH TIED TO PHILIPPE TO THE W.
SCATTERED MODERATE/ISOLATED STRONG CONVECTION COVERS THE AREA
WITHIN 90 NM OF LINE FROM 19N43W-21N47W.

W CARIBBEAN TROPICAL WAVE IS ALONG 81W/82W S OF 18N MOVING W 15
KT. WAVE HAS BECOME DEFINED OVER THE PAST SEVERAL HOURS WITH THE
ASSOCIATED SHOWERS/ISOLATED THUNDERSTORMS BEING S OF 13N W OF
81W TO INLAND OVER PANAMA TO S NICARAGUA.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 9N13W 13N24W...THEN ALONG 9N28W
16N41W...THEN BECOMES DISTORTED BY THE LOW/TROUGH AND HURRICANE
PHILIPPE. SCATTERED MODERATE/STRONG CONVECTION IS WITHIN 90 NM
OF THE AXIS FROM 36W-41W. CLUSTERS OF SCATTERED
MODERATE/ISOLATED STRONG CONVECTION ARE MOVING OFF AFRICA FROM
5N-10N E OF 16W.

...DISCUSSION...

GULF OF MEXICO...
STRONG UPPER HIGH CONTINUES TO DOMINATE GULF AND REMAINS
CENTERED OVER SE TEXAS STRETCHING FROM GEORGIA/ALABAMA BORDER
INTO NW MEXICO N OF 30N. THE STRONGEST SUBSIDENCE IS LOCATED
NEAR THE HIGH CENTER IN S TEXAS...BUT DRY AIR HAS BEEN ADVECTED
WELL S TO NEAR 23N. THE DRIEST ARE IS IN THE NW GULF AS UPPER
MOISTURE MOVES INTO THE AREA THANKS TO T.S. RITA. THE UPPER
TROUGH IN THE NW CARIBBEAN EXTENDS OVER THE YUCATAN CHANNEL AND
PENINSULA BRINGING WITH IT MOIST TROPICAL AIR RESULTING IN
SCATTERED SHOWERS/THUNDERSTORMS TO DEVELOPED OVER THE YUCATAN
PENINSULA MOVING ACROSS THE BAY OF CAMPECHE AND S ISOLATED
SHOWERS EXTEND N OF THIS AREA TO 23N W OF 90W. THE AREA FROM S
FLORIDA TO OVER CUBA W OF 83W IS BEGINNING TO EXPERIENCE
SHOWERS/THUNDERSTORMS OF THE RAINBANDS ASSOCIATED WITH T.S.
RITA. CONDITIONS WILL CONTINUE TO DETERIORATE TONIGHT AND
THROUGH TUE AS THE HEAVIEST CONVECTION MAKES ITS WAY ACROSS THE
FLORIDA KEYS INTO THE SE GULF AND WILL CONTINUE TO SPREAD
WESTWARD AS RITA MOVES ACROSS THE GULF.

CARIBBEAN...
AN ELONGATED UPPER LEVEL LOW IS CENTERED BETWEEN JAMAICA AND THE
CAYMAN ISLANDS BUT EXTENDS BEYOND THE YUCATAN CHANNEL AND E TO
THE WINDWARD PASSAGE AND HAITI...ON THE UNDERSIDE OF T.S. RITA.
ISOLATED SHOWERS EXTEND S OF THE UPPER LOW FROM THE CAYMANS SW
TO THE GULF OF HONDURAS. N OF THE UPPER LOW IS EXPERIENCING
SHOWERS/THUNDERSTORMS OF THE RAINBANDS ASSOCIATED WITH T.S. RITA.
AN UPPER HIGH IS CENTERED NEAR THE PANAMA CANAL WITH BROAD
ANTICYCLONIC FLOW REACHING N TO 16N AND THE ASSOCIATED UPPER
DIFFLUENCE IS FOSTERING THE SHOWERS/THUNDERSTORMS W OF THE
TROPICAL WAVE. RELATIVELY DRY AIR REMAINS ENTRENCHED OVER THE
CENTRAL CARIBBEAN BETWEEN 63W-75W WITH LITTLE IN THE WAY OF
SHOWERS EXCEPT IN THE VICINITY OF THE LESSER ANTILLES TO PUERTO
RICO WHERE SCATTERED SHOWERS/ISOLATED THUNDERSTORMS ARE FORMING
N AND E OF THE ISLANDS AND MOVING INTO THE CARIBBEAN.

ATLANTIC...
AN UPPER LEVEL SHEAR AXIS LIES ALONG THE N PERIPHERY OF T.S.
RITA FROM DAYTONA BEACH FLORIDA NE TO 30N74W...AND IS
NARROWING THE RIDGE AXIS WHICH IS PROVIDING AN OUTFLOW CHANNEL
FOR THE N SEMICIRCLE OF THE STORM. AN UPPER LOW IS ROTATING
W NEAR 27N58W WITH MOISTURE WRAPPING AROUND THE S AND E SIDE
OF THE CIRCULATION...AND COMBINING WITH THE OUTFLOW OF HURRICANE
PHILIPPE. THIS OUTFLOW IS ALSO BEING ENHANCED BY AN UPPER RIDGE
OVER THE TROPICS FROM 11N61W TO 20N48W WITH THE STRONGER UPPER
LEVEL WESTERLIES ESTABLISHED N OF THAT. ELSEWHERE...AN UPPER
LEVEL LOW IS CENTERED JUST SE OF THE AZORES AND THE ASSOCIATED
TROUGH DRAPES SW INTO THE AREA ALONG 32N27W-27N38W. THE BELT OF
WESTERLIES LIES BETWEEN 17N-26N WITH MAXIMUM JET CORE SPEEDS TO
70 KT AS OBSERVED IN SATELLITE-DERIVED WINDS. A RIDGE AXIS LIES
ALONG 15N ACROSS THE E/CENTRAL ATLC THEN NE TO THE MAURITANIA/
WESTERN SAHARA BORDER. THE TROPICAL WAVE ALONG 42W/43W IS THE
LEADING EDGE OF AN EASTERLY SURGE AND HAS BROUGHT A PLUME OF
SAHARAN DUST ACROSS THE AREA FROM 12N-23N E OF 40W.

$$
WALLACE


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