[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 131203
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT MON 13 SEP 2004

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH AMERICA...AND ATLC 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1115 UTC.

...SPECIAL FEATURE...
HURRICANE IVAN IS CENTERED NEAR 20.4N 84.1W OR 110 MILES SE OF
THE WESTERN TIP OF CUBA AT 13/1200 UTC MOVING WNW AT 8 KT.
MAXIMUM SUSTAINED WIND SPEED IS 140 KT WITH GUSTS TO 170 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 919 MB. SEE LATEST NHC
PUBLIC ADVISORY OR NHC FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS
MIATCPAT4/WTNT34 KNHC OR MIATCMAT4/WTNT24 KNHC FOR MORE DETAILS.
IVAN IS NOT AS SYMMETRICAL AS OF A FEW HOURS AGO AND THE EYE HAS
DEVELOPED. NUMEROUS STRONG CONVECTION IS WITHIN 120/140 NM FROM
THE CENTER EXCEPT IN THE NW QUADRANT WHERE IT IS ONLY 75 NM.
OUTER RAINBANDS EXTEND WITHIN 200 NM OF LINE FROM THE STRAITS OF
FLORIDA NEAR 24N80W ACROSS CUBA TO OVER HONDURAS NEAR 15N86W.
HEAVY RAIN AND THUNDERSTORMS ARE OVER THE CAYMAN ISLANDS. IN THE
UPPER LEVELS...IVAN IS FLANKED BY A MID/UPPER LEVEL TROUGH TO
THE NORTH AND STRONG MID/UPPER LEVEL RIDGING TO THE EAST.
SOUTHEAST FLOW IS TO THE IMMEDIATE W OF IVAN. THIS IS LIMITING
OUTFLOW TO THE W BUT THE REMAINDER OF THE PATTERN  CONTINUES TO
PROVIDE EXCELLENT OUTFLOW OVER THE REMAINDER OF THE QUADRANTS.
OTHERWISE...THE ATMOSPHERE REMAINS FAVORABLE AND IVAN SHOULD
REMAIN A MAJOR HURRICANE AS IT MOVES INTO THE GULF OF MEXICO.

...TROPICAL WAVES...
TROPICAL WAVE OVER THE E ATLC ALONG 38W/39W S OF 27N MOVING W AT
10 KT. VERY LARGE WAVE WITH THE CLASSIC SIGNATURE IN SATELLITE
IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN
150 NM OF LINE FROM 28N29W-23N38W.

TROPICAL WAVE APPROXIMATELY 90 NM E OF BARBADOS ALONG 59W S OF
20N MOVING W 10-15 KT. SCATTERED MODERATE/STRONG CONVECTION IS
WITHIN 60 NM OF 15N FROM 56W-60W. CLUSTERS OF SCATTERED
MODERATE/ISOLATED STRONG CONVECTION IS OVER A BROAD AREA FROM
13N-21N BETWEEN 54W-61W. THIS ACTIVITY WILL BE MOVING INTO THE
LEEWARD ISLANDS OVER THE NEXT FEW HOURS.

TROPICAL WAVE IN THE E CARIBBEAN ALONG 70W/71W S OF 20N MOVING W
10-15 KT. WAVE IS NOT AS DISCERNIBLE IN THE CARIBBEAN DUE TO THE
UPPER LEVEL RIDGE OVER THE AREA BUT A SMALL PORTION OF CURVATURE
IS OBSERVED JUST N OF HISPANIOLA. NO ASSOCIATED DEEP CONVECTION.

...ITCZ...
ITCZ AXIS EXTENDS ALONG 17N10W 11N25W 12N37W 7N49W 10N62W. LARGE
CLUSTERS OF SCATTERED MODERATE/ISOLATED STRONG CONVECTION ARE
FROM 2N-11N E OF 45W TO INLAND OVER AFRICA.

...DISCUSSION...

GULF OF MEXICO...
DEEP LAYERED TROUGH COVERS THE EAST HALF OF THE UNITED STATES
WITH A STRONG UPPER LEVEL LOW MOVING NE FROM THE UPPER
MISSISSIPPI VALLEY. WATER VAPOR IMAGERY SHOWS THAT THIS TROUGH
CONTINUES TO AMPLIFY SOUTH RESULTING IN A WEAKENING OF THE
MID/UPPER LEVEL RIDGE CURRENTLY IN PLACE ACROSS MUCH OF THE
GULF. THIS WILL GRADUALLY ALLOW HURRICANE IVAN TO TURN MORE TO
THE NORTHWEST EARLY TODAY WITH THE POWERFUL HURRICANE REACHING
THE SE GULF IN THE NEXT 12 TO 24 HOURS. CURRENTLY...GOOD UPPER
LEVEL DYNAMICS/LIFT AHEAD OF THE AMPLIFYING TROUGH IS PRODUCING
A LARGE AREA OF SCATTERED SHOWERS/THUNDERSTORMS ALONG A LOW
LEVEL TROUGH EXTENDING INLAND OVER TEXAS AND MEXICO.
ADDITIONALLY...STRONG SUBSIDENCE CONTINUES TO PUSH SE OVER THE
CENTRAL UNITED STATES IS MOVING ACROSS LOUISIANA INTO THE NW
GULF AND MISSISSIPPI.

CARIBBEAN...
THE MAIN FEATURE OVER THE CARIBBEAN IS HURRICANE IVAN WHICH IS
150 NM WNW OF GRAND CAYMAN ISLAND AND 120 NM SSE OF THE WESTERN
TIP OF CUBA. IVAN CONTINUES TO MOVE SLOWLY WNW OWING TO A
PERSISTENT MID LEVEL RIDGE WHICH EXTENDS ACROSS FLORIDA. THIS
RIDGE IS EXPECTED TO CONTINUE TO WEAKEN ALLOWING A MORE
NORTHWEST TURN EARLY TODAY TAKING IVAN TOWARD THE W TIP OF CUBA
AND THE YUCATAN CHANNEL. SEE SPECIAL FEATURES.
ELSEWHERE...STRONG MID/UPPER LEVEL RIDGING INDUCED BY OUTFLOW
FROM IVAN DOMINATES THE REMAINDER OF THE CARIBBEAN WITH
ASSOCIATED MODERATE SUBSIDENCE PRODUCING RATHER TRANQUIL/DRY
WEATHER. HOWEVER...A TROPICAL WAVE ABOUT 90 NM E OF BARBADOS
SHOULD BRING SHOWERS/ THUNDERSTORMS TO THE LESSER ANTILLES
WITHIN THE NEXT 12 HOURS.

SUBTROPICAL ATLANTIC...
A TROUGH-RIDGE-TROUGH PATTERN PREVAILS ACROSS MUCH OF THE
SUBTROPICAL ATLC. A MID/UPPER LEVEL LOW REMAINS OVER THE W ATLC
NEAR BERMUDA. THE UPPER LOW EXTENDS A TROUGH S TO JUST N OF THE
VIRGIN ISLANDS. ASSOCIATED MODERATE SUBSIDENCE AND DRY AIR
COVERS THE AREA WITHIN 125 NM OF LINE FROM 25N65W-28N72W
LIMITING SIGNIFICANT CLOUDS/CONVECTION. AT THE SURFACE...A WEAK
TROUGH EXTENDS FROM 175 NM WSW OF BERMUDA NEAR 31N68W TO OVER
THE SE BAHAMAS NEAR 22N74W. E OF THE UPPER LOW...DIFFLUENT FLOW
IN THE MID/UPPER LEVELS IS PRODUCING A LARGE AREA OF CLOUDINESS
AND SCATTERED SHOWERS/THUNDERSTORMS N OF 24N FROM 54W-65W. THERE
ARE NO SIGNS OF ORGANIZATION OR DEVELOPMENT WITH THIS ACTIVITY.
FURTHER E...MID/UPPER LEVEL RIDGE EXISTS OVER THE CENTRAL ATLC
ALONG 55W WITH THE MID-OCEANIC TROUGH LIMITED TO THE E ATLC FROM
BEYOND 32N33W TO 18N45W. OVER THE FAR E ATLC...A WELL DEFINED
MID/UPPER LEVEL HIGH IS OFF THE COAST OF AFRICA NEAR 16N18W WITH
ANTICYCLONIC FLOW E OF 33W.

TROPICAL ATLANTIC...
TROPICAL ATLC IS UNDER THE INFLUENCE OF A MID/UPPER RIDGE AXIS
EXTENDING FROM MID/UPPER LEVEL HIGH IS CENTERED OFF THE COAST OF
AFRICA NEAR 16N18W W INTO THE E CARIBBEAN ALONG 15N/17N. A WEAK
TROUGH SPLITS THE RIDGE NEAR 38W. ELSEWHERE...DEEP LAYERED ELY
FLOW PREVAILS.

$$
WALLACE



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