[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 172356
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN SEP 17 2006

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH AMERICA...AND THE 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...
THE CENTER OF HURRICANE GORDON WAS NEAR 34.6N 52.4W OR ABOUT OR
ABOUT 1430 MILES WEST OF THE AZORES AT 17/2100. GORDON IS MOVING
TOWARD THE NORTH-NORTHEAST AT 12 KT. THE ESTIMATED MINIMUM
CENTRAL PRESSURE IS 983 MB. THE MAXIMUM SUSTAINED WIND SPEEDS
ARE 70 KT WITH GUSTS TO 85 KT. PLEASE READ THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
OR THE PUBLIC ADVISORY UNDER MIATCPAT2/WTNT32 KNHC FOR MORE
DETAILS. SCATTERED MODERATE CONVECTION IS ASSOCIATED WITH GORDON
MAINLY NORTH OF THE CENTER FROM 34N-37N BETWEEN 50W-53W. GORDON
IS EXPECTED TO BECOME EXTRATROPICAL IN ABOUT TWO DAYS NEAR THE
AZORES AS IT MERGES WITH A FRONTAL SYSTEM.

THE CENTER OF HURRICANE HELENE WAS NEAR 21.2N 49.3W...OR ABOUT
920 NM EAST-NORTHEAST OF THE NORTHERN LEEWARD ISLANDS. HELENE
IS MOVING NORTHWEST 8 KT. THE ESTIMATED MINIMUM CENTRAL PRESSURE
IS 970 MB. THE MAXIMUM SUSTAINED WIND SPEEDS ARE 90 KT WITH
GUSTS TO 110 KT. PLEASE READ THE LATEST NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC OR THE PUBLIC
ADVISORY UNDER MIATCPAT2/ WTNT32 KNHC FOR MORE DETAILS. A BAND
OF MODERATE TO STRONG CONVECTION IS MAINLY ON THE WESTERN SIDE
OF THE HURRICANE FROM 19N-23N BETWEEN 48W-51W. SOME
STRENGTHENING IS POSSIBLE DURING THE NEXT 24-36 HOURS AND HELENE
MAY BECOME THE SECOND MAJOR HURRICANE OF THE SEASON.

...TROPICAL WAVES...
AN ATLANTIC OCEAN 1012 MB LOW PRESSURE CENTER IS NEAR
18N23W...JUST NORTH OF THE CAPE VERDE ISLANDS. SHOWER ACTIVITY
ASSOCIATED WITH THIS BROAD AREA OF LOW PRESSURE HAS DIMINISHED
AND PROBABLY ONLY AN OPEN WAVE LEFT IN THIS AREA. BASED ON
THAT...A TROPICAL WAVE WAS ADDED ALONG 22/23W ON THE 1800 UTC
MAP.

AS OF 2100 UTC...A TROPICAL WAVE IS ENTERING THE YUCATAN
PENINSULA. IT AXIS LIES ALONG 87/88W. THE WAVE IS ENHANCING THE
SHOWER/TSTM ACTIVITY OVER NICARAGUA...HONDURAS...THE YUCATAN
PENINSULA AND NORTHERN GUATEMALA. THERE ARE ALSO SCATTERED
SHOWERS OVER THE NW CARIBBEAN CARIBBEAN JUST BEHIND THE WAVE
AXIS.

THE NORTHERN END OF A TROPICAL WAVE IS MOVING THROUGH SOUTHERN
MEXICO...NOW OVER THE AREA JUST WEST OF THE ISTHMUS OF
TEHUANTEPEC. SCATTERED SHOWERS AND TSTMS ARE OVER CHIAPAS AND
OAXACA IN MEXICO NEAR THE WAVE AXIS.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 11N12W 12N21W 10N30W 12N44W
13N48W 10N60W. CLUSTERS OF SCATTERED MODERATE/STRONG CONVECTION
ARE INLAND JUST NORTH OF THE ITCZ BETWEEN 11W-17W. SIMILAR
CONVECTION IS FOUND FROM 6N-10N BETWEEN 18W-20W.

...DISCUSSION...

THE GULF OF MEXICO...
AN UPPER RIDGE COVERS THE ENTIRE GULF AND THE SE U.S. INCLUDING
THE STATE OF FLORIDA. ABUNDANT DRY MID TO UPPER LEVEL AIR COVERS
THE AREA. THERE ARE ISOLATED SHOWERS OVER THE NORTHERN GULF
WATERS N OF 27N AND WEST OF 85W. SCATTRED SHOWERS AND TSTMS ARE
ALSO ALONG THE FLORIDA WEST COAST MAINLY SOUTH OF TAMPA BAY. A
DIFFLUENT PATTERN ALOFT BETWEEN THE RIDGE OVER THE GULF AND A
TROUGH OFF THE U.S. EAST COAST IS ENHANCING THIS SHOWER
ACTIVITY. AT THE SURFACE...SELY WINDS OF 10-15 KT DOMINATES THE
GULF AHEAD OF A NEW COLD FRONT THAT IS EXPECTED TO MOVE IN LATE
MON AFTERNOON OR EARLY EVENING...INCREASING THE LIKELIHOOD OF
SHOWERS OVER THE NORTHERN GULF WATERS.

THE CARIBBEAN SEA...
AN UPPER ANTICYCLONE IS OVER THE NW CARIBBEAN NEAR 17N83W
SUPPORTING THE DEVELOPMENT OF CONVECTIVE ACTIVITY OVER CENTRAL
AMERICA AND THE SW CORNER OF THE AREA. ANOTHER UPPER ANTICYCLONE
IS SITUATED JUST EAST OF THE LESSER ANTILLES. ABUNDANT DRY
AIR...RESULTING IN MODERATE TO STRONG SUBSIDENCE DOMINATES THE
EASTERN CARIBBEAN INCLUDING PUERTO RICO AND DOMINICAN REPUBLIC
AS WELL AS THE LESSER ANTILLES. THE UW-CIMMS SAHARAN AIR LAYER
ANALYSIS ALSO SUGGESTS THIS AREA IS UNDER THE INFLUENCE OF
SAHARAN DUST. UPPER LEVEL MOISTURE IS BEING ADVECTED OVER
VENEZUELA. AN INVERTED TROUGH LIES BETWEEN THESE TWO
ANTICYCLONES ALONG 71W. MODERATE TO STRONG WINDS ARE BLOWING
ACROSS THE BASIN. THE STRONGEST WINDS OF 2O KT ARE SEEN JUST
NORTH OF WESTERN VENEZUELA AND NORTHERN COLOMBIA. SCATTERED
MODERATE CONVECTION OVER THE SW CORNER OF THE AREA AND OVER
COSTA RICA AND PANAMA DUE TO THE CLOSE PROXIMITY OF THE ITCZ.

THE ATLANTIC OCEAN...
THE DEEP LAYER TROUGH LOCATED OFF THE U.S. EAST COAST EXTENDS
SOUTHWESTWARD ALONG THE NORTHERN BAHAMAS AND WESTERN CUBA. A
SURFACE TROUGH RUNS FROM 26N72W TO 24N80W. SHOWERS AND TSTMS
HAVE FORMED ALONG CUBA JUST EAST OF THIS UPPER TROUGH. THE
ASSOCIATED FRONTAL SYSTEM IS A WEAKENING COLD FRONT THAT EXTENDS
FROM A 1008 MB LOW PRESSURE LOCATED NORTH OF THE AREA NEAR
35N70W TO 26N72W. ISOLATED SHOWERS ARE RELATED TO THE FRONTAL
BOUNDARY. A MID TO UPPER LEVEL HIGH IS EAST OF THE LEEWARD
ISLANDS NEAR 15N58W. SATELLITE IMAGERY SHOWS THE OUTFLOW OF
HURRICANE HELENE OVER THE CENTRAL ATLC. A CUT-OFF LOW IS LOCATED
NEAR 23N31W. EAST OF THE LOW THERE IS AN UPPER ANTICYCLONE
COVERING WESTERN AFRICA AND THE FARTHER EAST ATLANTIC OCEAN. AT
THE SURFACE...A RIDGE DOMINATES THE E ATLC FROM A 1024 MB HIGH
ANCHORED WITHIN AROUND 200 NM NORTH OF MADEIRA ISLANDS. ISOLATED
TO SCATTERED SHOWERS ARE NORTH OF 22N AND EAST OF 25W...JUST
EAST OF THE UPPER TROUGH AXIS MENTIONED ABOVE.

$$
GR



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