[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 130603
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0345 UTC.

...SPECIAL FEATURE...
HURRICANE IVAN IS CENTERED NEAR 19.9N 83.5W OR 160 MILES SE OF
THE WESTERN TIP OF CUBA AT 13/0600 UTC MOVING WNW AT 8 KT.
MAXIMUM SUSTAINED WIND SPEED IS 140 KT WITH GUSTS TO 170 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 917 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 CONTINUES TO DEMONSTRATE A VERY SYMMETRICAL APPEARANCE BUT
THE EYE HAS FILLED IN OVER THE PAST 6 HOURS. NUMEROUS STRONG
CONVECTION IS WITHIN 150 NM IN THE S SEMICIRCLE AND WITHIN 90 NM
IN THE N SEMICIRCLE. OUTER RAINBANDS EXTEND FROM 15N-23N
INCLUDING PORTIONS OF HONDURAS...JAMAICA...AND CUBA. THE CAYMAN
ISLANDS ARE STILL UNDER THE INFLUENCE OF IVAN. IN THE UPPER
LEVELS...IVAN IS FLANKED BY A WEAK UPPER LEVEL TROUGH TO THE
WEST AND STRONG MID/UPPER LEVEL RIDGING TO THE EAST. THIS
PATTERN CONTINUES TO PROVIDE EXCELLENT OUTFLOW IN ALL BUT THE NW
QUADRANT WHERE WATER VAPOR IMAGERY SHOWS MODERATE SUBSIDENCE
OVER THE SW GULF FROM S FLORIDA TO THE YUCATAN PENINSULA.
OTHERWISE...THE ATMOSPHERE LOOKS GENERALLY FAVORABLE AND IVAN
SHOULD REMAIN A MAJOR HURRICANE AS IT MOVES TOWARD W CUBA.

...TROPICAL WAVES...
TROPICAL WAVE OVER THE E ATLC ALONG 37W/38W S OF 24N MOVING W
NEAR 15 KT. VERY LARGE WAVE WITH THE CLASSIC SIGNATURE IN
SATELLITE IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION
IS ALONG THE N PORTION WITHIN 75 NM OF LINE FROM 21N34W-24N36W.

TROPICAL WAVE APPROXIMATELY 100 NM E OF BARBADOS ALONG 57W/58W S
OF 20N MOVING W NEAR 20 KT. SCATTERED MODERATE/ISOLATED STRONG
CONVECTION IS E OF THE WAVE FROM 13N-17N BETWEEN 50W-55W.

TROPICAL WAVE IN THE E CARIBBEAN ALONG 68W/69W S OF 20N MOVING W
10-15 KT. WAVE IS NOT AS DISCERNIBLE IN THE CARIBBEAN DUE TO THE
UPPER RIDGE OVER THE AREA BUT A SMALL PORTION OF CURVATURE IS
OBSERVED JUST N OF PUERTO RICO AND THE MONA PASSAGE. NO
ASSOCIATED DEEP CONVECTION.

...ITCZ...
ITCZ AXIS EXTENDS ALONG 11N15W 9N25W 10N36W 8N41W 11N60W.
SCATTERED MODERATE/STRONG CONVECTION IS FROM 6N-10N BETWEEN
29W-35W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS INLAND
AND WITHIN 75 NM ALONG THE COAST OF AFRICA FROM 5N-9N. CLUSTERS
OF SIMILAR CONVECTION ARE FROM 5N-10N BETWEEN 25W-29W AND
35W-47W. CLUSTERS OF SCATTERED MODERATE CONVECTION ARE FROM
2N-10N BETWEEN 13W-25W.

...DISCUSSION...

GULF OF MEXICO...
DEEP LAYERED TROUGH COVERS THE EAST HALF OF THE UNITED STATES
WITH A STRONG UPPER LEVEL LOW OVER THE 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 EVOLUTION IS
EXPECTED TO ALLOW HURRICANE IVAN TO GRADUALLY TURN MORE TO THE
NORTH EARLY TODAY WITH THE POWERFUL HURRICANE REACHING THE SE
GULF IN THE NEXT 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 ALONG THE TEXAS/MEXICO COAST INTO THE BAY OF
CAMPECHE. SIMILAR ACTIVITY IS IN THE NE GULF N OF 27N E OF 90W.
ADDITIONALLY...STRONG SUBSIDENCE OVER THE CENTRAL UNITED STATES
IS MOVING ACROSS TEXAS AND LOUISIANA INTO THE NW GULF.

CARIBBEAN...
THE MAIN FEATURE OVER THE CARIBBEAN IS HURRICANE IVAN WHICH IS
100 NM WNW OF GRAND CAYMAN ISLAND. 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 NORTHWARD TURN EARLY TODAY TAKING IVAN TOWARD THE W TIP OF
CUBA. SEE SPECIAL FEATURES. ELSEWHERE...STRONG MID/UPPER LEVEL
RIDGING INDUCED BY OUTFLOW FROM IVAN DOMINATES THE E TWO-THIRDS
OF THE CARIBBEAN WITH ASSOCIATED SUBSIDENCE PRODUCING RATHER
TRANQUIL/DRY WEATHER. HOWEVER...A TROPICAL WAVE ABOUT 100 NM E
OF BARBADOS SHOULD BRING SHOWERS/THUNDERSTORMS TO THE LESSER
ANTILLES IN 12 HOURS.

SUBTROPICAL ATLANTIC...
A TROUGH-RIDGE-TROUGH PATTERN PREVAILS ACROSS MUCH OF THE
SUBTROPICAL ATLC. A MID/UPPER LEVEL LOW WHICH SPLIT OFF THE
MID-OCEANIC TROUGH SEVERAL DAYS AGO 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 150 NM OF LINE FROM 23N65W-28N74W
LIMITING SIGNIFICANT CLOUDS/CONVECTION. E OF THE UPPER LOW...
DIFFLUENT FLOW IN THE MID/UPPER LEVELS IS PRODUCING A LARGE AREA
OF CLOUDINESS AND SCATTERED SHOWERS/STRONG THUNDERSTORMS FROM
22N-34N BETWEEN 54W-63W. THERE ARE NO SIGNS OF ORGANIZATION OR
DEVELOPMENT WITH THIS ACTIVITY. FURTHER E...MID/UPPER LEVEL
RIDGE EXISTS OVER THE CENTRAL ATLC ALONG 54W WITH THE
MID-OCEANIC TROUGH LIMITED TO THE E ATLC FROM BEYOND 32N29W TO
18N46W. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS WITHIN
90 NM OF 31W FROM 25N-30N. AT THE SURFACE...A TROUGH EXTENDS
FROM 26N37W TO BEYOND 34N34W. OVER THE FAR E ATLC...A WELL
DEFINED MID/UPPER LEVEL HIGH IS CENTERED NEAR ALONG THE COAST OF
AFRICA NEAR 17N15W E OF 35W.

TROPICAL ATLANTIC...
TROPICAL ATLC IS UNDER THE INFLUENCE OF A MID/UPPER RIDGE AXIS
EXTENDING FROM MID/UPPER LEVEL HIGH IS CENTERED NEAR ALONG THE
COAST OF AFRICA NEAR 17N15W W INTO THE E CARIBBEAN ALONG
15N/17N. A WEAK TROUGH SPLITS THE RIDGE NEAR 37W.
ELSEWHERE...DEEP LAYERED ELY FLOW PREVAILS.

$$
WALLACE


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