[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 241751
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN SEP 24 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...SPECIAL FEATURES...
SATELLITE IMAGES AND OTHER DATA INDICATE THAT HELENE HAS LOST ITS
TROPICAL CHARACTERISTICS AND IT IS NOW AN EXTRATROPICAL CYCLONE.
IT IS CENTERED NEAR 40.9N 37.5W OR ABOUT 595 NM WEST-NORTHWEST
OF THE AZORES AT 24/1500 UTC MOVING NORTHEAST AT 18 KT.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 970 MB. MAXIMUM SUSTAINED
WIND SPEED IS 60 KT WITH GUSTS TO 75 KT. SEE THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT3/WTNT23 KNHC
FOR MORE DETAILS. CONVECTION CONTINUES TO SLOWLY WEAKEN NEAR THE
CENTER OF HELENE. THE SYSTEM HAS ACQUIRED DEFINITIVE FRONTAL
FEATURES WITH EXTENSIVE COLD AIR ADVECTION OVER THE SOUTHWESTERN
SEMICIRCLE AS EVIDENCED BY THE LARGE STRATOCUMULUS FIELD.
DENSE OVERCAST CLOUDS WITH SHOWERS/THUNDERSTORMS IS N OF 38N
FROM 34W-39W. THE CENTER OF THE SYSTEM IS FORECAST TO PASS WELL
TO THE NORTH OF THE AZORES AS AN EXTRATROPICAL LOW. GALE FORCE
WINDS COULD IMPACT PORTIONS OF THE AZORES LATER TODAY OR TONIGHT.
THE LAST ADVISORY WAS ISSUED AT 1500 UTC.

...TROPICAL WAVES...
A NEW TROPICAL WAVE IS ADDED ON THE 1200 UTC MAP ALONG 22W SOUTH
OF 13N BASED ON SATELLITE IMAGERY...SURFACE DATA AND UPPER AIR.
SOME CYCLONIC TURNING IS EVIDENT AT LOW LEVELS. MOST OF THE
CONVECTIVE ACTIVITY IS AHEAD OF THE WAVE AXIS. SCATTERED
MODERATE TO ISOLATED STRONG CONVECTION IS FROM 6N-10N BETWEEN
22W-27W.

A 1009 MB LOW IS CENTERED NEAR 18.9N43.7W NEAR STATIONARY. LOW
LEVEL CENTER IS SW OF THE ASSOCIATED DEEP CONVECTION. SCATTERED
MODERATE/STRONG CONVECTION IS FROM 16N-21N BETWEEN 39W-42W.
UPPER-LEVEL WINDS ARE ONLY MARGINALLY FAVORABLE FOR TROPICAL
CYCLONE FORMATION IN THIS AREA. HOWEVER...ONLY A SLIGHT INCREASE
IN THE ORGANIZATION OF THIS SYSTEM WOULD RESULT IN THE FORMATION
OF A TROPICAL DEPRESSION LATER TODAY OR ON MONDAY AS IT DRIFTS
GENERALLY NORTHWESTWARD.

TROPICAL WAVE IS ALONG 48W S OF 17N MOVING W 10 KT. WEAK WAVE
EMBEDDED WITHIN DRY AIR AND HAS NO ASSOCIATED CONVECTION.

TROPICAL WAVE IS OVER THE LESSER ANTILLES ALONG 62W S OF 20N
MOVING SLOWLY WESTWARD AT AROUND 10KT. BROADENING INVERTED-V
SIGNATURE CURVATURE WITH SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS FROM 13N-18N BETWEEN 58W-64W. THIS WAVE WILL
MOVE ACROSS THE VIRGIN ISLANDS AND PUERTO RICO LATE TODAY TROUGH
MONDAY AND IS EXPECTED TO REACH DOMINICAN REPUBLIC MONDAY
AFTERNOON OR EVENING...INCREASING THE CHANCE OF RAIN OVER THOSE
ISLANDS.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 9N14W 7N25W 10N40W 10N50W 12N60W.
OUTSIDE FROM THE CONVECTION ASSOCIATED WITH THE TROPICAL
WAVES...CLUSTERS OF SCATTERED MODERATE/ ISOLATED STRONG
CONVECTION ARE ALONG THE COAST OF LIBERIA AND SIERRA LEONE IN
AFRICA AND NEAR 6N18W.

...DISCUSSION...
GULF OF MEXICO...
THE MAIN FEATURE ACROSS THE GULF TODAY IS THE COLD FRONT MOVING
OFF THE TEXAS COAST. AS OF 1500 UTC...THE FRONT EXTENDS ALONG
32N90W 28N96W INTO THE DEEP SOUTH TEXAS AND NORTHERN MEXICO. A
SQUALL LINE WITH GUSTY WINDS OF 30-35 KT MOVED ACROSS SOUTH
TEXAS AND NE MEXICO THIS MORNING. A DIFFLUENT PATTERN ALOFT WAS
ENHANCING THE THUNDERSTORM ACTIVITY OVER THIS AREA. A CLUSTER OF
MODERATE CONVECTION IS STILL AFFECTING NE MEXICO. A BROAD UPPER
TROUGH THAT EXTENDS FROM AN UPPER LOW MOVING ACROSS THE GREAT
LAKES TO TEXAS IS SUPPORTING THIS STRONG COLD FRONT. AN UPPER
HIGH IS CENTERED OVER NE MEXICO NEAR 25N99W WITH A BROAD RIDGE
COVERING THE W GULF W OF 91W. ANOTHER UPPER HIGH IS ANCHORED IN
THE W ATLC EXTENDING A RIDGE OVER THE E GULF E OF 85W AND THE
STATE OF FLORIDA. AN UPPER LOW REMAINS BETWEEN THESE RIDGES AND
IS CENTERED OVER THE NE PORTION OF THE YUCATAN PENINSULA NEAR
21N88W. THIS FEATURE IS GENERATING SCATTERED SHOWERS/ISOLATED
THUNDERSTORMS OVER THE YUCATAN PENINSULA/CHANNEL AND WESTERN
CUBA. MODERATE TO STRONG WINDS OF 20-25 KT WILL FOLLOW THE COLD
FRONT AS IT MOVES SEWD ACROSS THE GULF. THE FRONT WILL EXTEND
FROM THE FL PANHANDLE TO NE MEXICO MONDAY MORNING.

CARIBBEAN SEA...
THE UPPER LOW CENTERED OVER THE YUCATAN PENINSULA COVERS A SMALL
PORTION OF NW CARIBBEAN N OF 18N W OF 85W. BROAD UPPER RIDGE
OVER FLORIDA AND THE W ATLC DIPS S OVER WEST-CENTRAL CUBA INTO
THE CARIBBEAN. THIS COMBINATION IS GENERATING SCATTERED
SHOWERS/ISOLATED THUNDERSTORMS N OF 15N W OF 74W. AN UPPER LOW
IS OVER HISPANIOLA WITH A TROUGH EXTENDING SW TO 14N79W. AN
UPPER HIGH IS NE OF THE LEEWARD ISLANDS NEAR 20N60W. THIS SYSTEM
IS ENHANCING THE SHOWER/TSTM ACTIVITY ASSOCIATED WITH THE
TROPICAL WAVE ENTERING THE EASTERN CARIBBEAN. MODERATE TRADE
WINDS AREA NOTED OVER THE BASIN.

ATLANTIC OCEAN...
BROAD UPPER RIDGE COVERS THE W ATLC ANCHORED BY AN UPPER HIGH
LOCATED JUST E OF FLORIDA. WEAK UPPER TROUGH EXTENDS FROM 31N44W
SW TO JUST E OF THE LEEWARD ISLANDS NEAR 16N55W. BROAD UPPER
HIGH SITUATED NW OF THE CAPE VERDE ISLANDS NEAR 18N35W COVERS
THE REMAINDER OF THE E ATLC. AT THE SURFACE...A COLD FRONT
ENTERS THE AREA NEAR 31N41W...THEN CONTINUES SOUTHWESTWARD TO
27N55W. A NARROW BAND OF LOW/MID CLOUDS WITH EMBEDDED SHOWERS IS
RELATED TO THE FRONT. THE W ATLC SURFACE RIDGE EXTENDS FROM A
1022 MB HIGH LOCATED NEAR 33N60W TO FLORIDA AND THE EXTREME SE
OF U.S..THE E ATLC RIDGE COVERS THE REGION N OF 20N WEST OF 35W
ANCHORED BY A 1019 NEAR 28N30W.

$$
GR






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