[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 182349
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT MON SEP 18 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 HELENE WAS NEAR 23.9N 51.1W OR ABOUT 870
MILES EAST-NORTHEAST OF THE NORTHERN LEEWARD ISLANDS AT 18/2100
UTC. HELENE IS MOVING WEST-NORTHWEST 8 KT. THE ESTIMATED MINIMUM
CENTRAL PRESSURE IS 960 MB. THE MAXIMUM SUSTAINED WIND SPEEDS
ARE 100 KT WITH GUSTS TO 120 KT. HELENE REMAINS A LARGE AND
POWERFUL CATEGORY THREE HURRICANE ON THE SAFFIR-SIMPSON
HURRICANE SCALE. PLEASE READ THE LATEST NHC FORECAST/ADVISORY
UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC OR THE PUBLIC
ADVISORY UNDER MIATCPAT3/ WTNT33 KNHC FOR MORE DETAILS. NUMEROUS
MODERATE TO STRONG CONVECTION IN A 60 NM-WIDE BAND EXTENDING
WEST OF THE CENTER FROM 22N-25N. HELENE IS FORECAST TO REMAIN
OUT TO SEA.

THE CENTER OF HURRICANE GORDON WAS NEAR 37.9N 43.3W OR ABOUT 880
MILES WEST OF TERCEIRA IN THE AZORES AT 19/0000 UTC. GORDON IS
MOVING QUICKLY TO EAST-NORTHEAST NEAR 24 KT. THE ESTIMATED
MINIMUM CENTRAL PRESSURE IS 975 MB. THE MAXIMUM SUSTAINED WIND
SPEEDS ARE 80 KT WITH GUSTS TO 100 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. NUMEROUS MODERATE TO STRONG CONVECTION ARE WITHIN A 50
NM RADIUS OF THE CENTER. GORDON THREATENS THE AZORES. A TROPICAL
STORM WATCH IS ALREADY IN EFFECT FOR THESE ISLANDS. THE TROPICAL
CYCLONE WILL BE NEAR OR OVER THE AZORES ON TUESDAY AFTERNOON OR
EVENING.

...TROPICAL WAVES...
A SURFACE TROUGH...REMNANT OF THE FORMER SURFACE LOW THAT WAS
NEAR THE CAPE VERDE ISLANDS YESTERDAY IS ALONG 28W FROM 18N TO
28N. SCATTERED SHOWERS AND TSTMS ARE JUST EAST OF THE TROUGH.

A TROPICAL WAVE IS ALONG 36W SOUTH OF 20N. VIS SATELLITE IMAGERY
SHOWS AN INVERTED V CLOUD PATTERN ASSOCIATED WITH THE WAVE.
SCATTERED SHOWERS ARE ON THE SOUTHERN END OF THE WAVE.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 8N13W 7N30W 8N40W CURVING
NORTHWARD TOWARD HURRICANE HELENE TO 12N45W. ANOTHER SEGMENT OF
THE ITCZ IS FROM 12N48W TO 9N60W. SCATTERED MODERATE TO ISOLATED
STRONG CONVECTION IS WITHIN 80 NM MAINLY SOUTH OF THE AXIS
BETWEEN 18W-28W AND BETWEEN 40W-46W.

...DISCUSSION...
A DEEP LAYER TROUGH IS OVER CENTRAL U.S. AND NORTHERN MEXICO
MOVING EWD. THE ASSOCIATED COLD FRONT EXTENDS FROM A 1010 MB
SURFACE LOW PRES LOCATED OVER ARKANSAS ACROSS SE TEXAS INTO
NORTHERN MEXICO. THIS SYSTEM IS FORECAST TO MOVE OFFSHORE THE
TEXAS COAST THIS EVENING AND WILL EXTEND FROM THE FLORIDA
PANHANDLE TO NE MEXICO ON TUESDAY. MODERATE N TO NE WINDS WILL
FOLLOW THE FRONTAL BOUNDARY THAT IS EXPECTED TO MOVE ACROSS THE
FLORIDA PENINSULA TUESDAY NIGHT/WEDNESDAY. MOISTURE AND THE
CHANCE OF SHOWERS WILL INCREASE AHEAD OF THE FRONT. AS OF 2100
UTC...A PRE-FRONTAL TROUGH RUNS FROM 28N92W TO NEAR TAMPICO
MEXICO. MUCH OF THE SHOWER ACTIVITY IS CURRENTLY BEHIND THIS
TROUGH. AN UPPER ANTICYCLONE IS NEAR 28N92W COVERING THE EASTERN
PORTION OF THE GULF. DRY AIR IS ON THE SOUTH SIDE OF THIS HIGH
FROM 21N-27N BETWEEN 87W-93W. ANOTHER UPPER ANTICYCLONE IS
SITUATED NEAR BELIZE AND COVERS SOUTH MEXICO AND THE YUCATAN
PENINSULA. SCATTERED SHOWERS AND TSTMS HAVE DEVELOPED UNDER THE
INFLUENCE OF THIS UPPER FEATURE. S TO SW WINDS OF 10-15 KT
DOMINATES THE GULF AHEAD OF THE COLD FRONT.

THE CARIBBEAN SEA...
AN UPPER ANTICYCLONE IS NEAR BELIZE SUPPORTING THE DEVELOPMENT
OF SCATTERED SHOWERS AND TSTMS OVER CENTRAL AMERICA AND THE
YUCATAN PENINSULA. ANOTHER UPPER ANTICYCLONE IS LOCATED OVER THE
LEEWARD ISLANDS WITH A RIDGE EXTENDING SOUTHWESTWARD ACROSS THE
ABC ISLANDS. ABUNDANT DRY AIR...RESULTING IN MODERATE TO STRONG
SUBSIDENCE DOMINATES THE EASTERN CARIBBEAN WEST OF 70W...
INCLUDING PUERTO RICO AND DOMINICAN REPUBLIC AS WELL AS ALL THE
LESSER ANTILLES. THE UW-CIMMS SAHARAN AIR LAYER IS STILL SHOWING
THAT 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 75W. THE TRADE
WINDS ARE ON THE WEAK SIDE...COMPARED WITH THE PREVIOUS DAYS
THANKS TO THE TROPICAL CYCLONE ACTIVITY OVER THE ATLANTIC OCEAN
THAT IS CREATING A BREAK IN THE SUBTROPICAL RIDGE. SCATTERED
MODERATE CONVECTION IS FOUND OVER COSTA RICA AND PANAMA DUE TO
THE CLOSE PROXIMITY OF THE ITCZ. CLUSTERS OF SCATTRED MODERATE
TO ISOLATED STRONG CONVECTION HAVE ALSO DEVELOPED OVER NORTHERN
VENZUELA AND COLOMBIA DUE TO A DIFFLUENT PATTERN ALOFT.

THE ATLANTIC OCEAN...
THE DEEP LAYER TROUGH LOCATED OVER THE W ATLC EXTENDS
SOUTHWESTWARD ALONG THE NORTHERN BAHAMAS AND WESTERN CUBA TO THE
NE PORTION OF THE YUCATAN PENINSULA. A SURFACE TROUGH RUNS ALONG
31N68W 24N74W 24N80W. SCATTERED SHOWERS AND TSTMS HAVE FORMED
NEAR THE BASE OF THE UPPER TROUGH OVER THE FLORIDA KEYS...THE
STRAIT OF FLORIDA AND ALONG CUBA. A MID TO UPPER LEVEL HIGH IS
OVER THE LEEWARD ISLANDS WITH A RIDGE EXTENDING NWD ALONG
60/61W. DRY AIR COVERS THE ATLANTIC OCEAN AND THE CARIBBEAN SEA
FROM 10N-27N BETWEEN 55W-70W. SATELLITE IMAGERY SHOWS THE
OUTFLOW OF HURRICANE HELENE OVER THE CENTRAL ATLC. A CUT-OFF LOW
IS LOCATED NEAR 20N32W. 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 1023 MB HIGH ANCHORED NEAR 33N32W. THIS SYSTEM IS
FORECAST TO MOVE SOUTH DURING THE NEXT 24 HOURS.

$$
GR




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