[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 121735
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN MAY 12 2013

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND 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.

...ITCZ/MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS FROM THE COAST OF SIERRA LEONE NEAR
8N13W TO 7N16W. THE INTERTROPICAL CONVERGENCE ZONE AXIS EXTENDS
FROM 4N20W TO EQ40W TO THE COAST OF BRAZIL AT 1N50W. SCATTERED
MODERATE CONVECTION IS NOTED FROM 4N TO 8N BETWEEN 15W-18W.
SIMILAR CONVECTION IS FROM 3N TO 6N BETWEEN 48W AND THE COAST OF
BRAZIL AND FRENCH GUIANA. ISOLATED MODERATE CONVECTION IS WITHIN
240 NM N OF ITCZ AXIS W OF 30W AND WITHIN 180 NM S OF AXIS
BETWEEN 28W AND 35W.

WIDELY SCATTERED MODERATE CONVECTION IS N OF THE ITCZ FROM 2N-7N
BETWEEN 48W-53W.

...DISCUSSION...

GULF OF MEXICO...

A WEAK LATE SEASON COLD FRONT EXTENDS FROM THE FLORIDA BIG BEND
ACROSS THE CENTRAL GULF TO NEAR TUXPAN MEXICO. A 90 NM WIDE BAND
OF SHOWERS AND TSTMS IS ASSOCIATED WITH THE FRONT S OF 26N.
WINDS W OF THE FRONT ARE NORTHERLY AT 10 TO 15 KT. HOWEVER...
BUOY 42002 JUST BEHIND THE FRONT IS REPORTING SUSTAINED WINDS OF
29 KT...LIKELY ASSOCIATED WITH THE STRONG CONVECTION. THE FRONT
IS FORECAST TO CONTINUE E AND EXTEND FROM CEDAR KEY FLORIDA TO
TO 18N93W TONIGHT...THEN IT WILL NEARLY STALL FROM SE FLORIDA TO
23N90W TO 19N93W ON MON. A PREFRONTAL SURFACE TROUGH IS ANALYZED
FROM NORTHERN FLORIDA THROUGH TAMPA BAY TO NEAR 25N85W. ANOTHER
TROUGH EXISTS IN THE BAY OF CAMPECHE AND EXTENDS NORTHEASTWARD
TO NEAR 22N92W ALSO AHEAD OF THE FRONT. SOME CONVECTION WAS
NOTED OVER SE MEXICO ON THE EAST SIDE OF THIS TROUGH...BUT
CURRENTLY IS WEAKENING. HIGH PRESSURE WILL BUILD IN THE WAKE OF
THE FRONT OVER THE GULF TONIGHT. IN THE UPPER LEVELS...AN UPPER
LEVEL RIDGE CONTINUES TO DOMINATE THE GULF. ABUNDANT MID/UPPER
LEVEL MOISTURE IS NOTE ON WATER VAPOR IMAGERY ACROSS MUCH OF THE
REGION.

CARIBBEAN SEA...

TRADE WIND FLOW OF 10-15 KT DOMINATES THE MAJORITY OF THE
EASTERN AND CENTRAL CARIBBEAN WITH WINDS OF 20 TO 25 KT NEAR THE
COAST OF COLOMBIA. THIS REGIMEN IS FORECAST TO PERSIST OVER THE
NEXT SEVERAL DAYS. A WEAK COLD FRONT WILL PASS E ACROSS CUBA AND
THE CARIBBEAN WATERS N OF 20N AND W OF HISPANIOLA ON MON AND
TUE. MODERATE TO FRESH NE WINDS WILL FOLLOW THE FRONT. LOW TOP
TRADE WIND SHOWERS ARE SEEN ON VIS SATELLITE PICTURES ACROSS
MOST OF THE BASIN. SCATTERED SHOWERS AND ISOLATED TSTMS ARE OVER
THE SW CARIBBEAN NEAR THE ATLC COAST OF COSTA RICA AND WESTERN
PANAMA. ALOFT...AN UPPER ANTICYCLONE CENTERED BETWEEN SAN ANDRES
AND PROVIDENCIA ISLANDS EXTENDS A RIDGE ACROSS THE WESTERN
CARIBBEAN PROVIDING MOSTLY FAIR CONDITIONS THERE. AN UPPER LEVEL
TROUGH PERSISTS ACROSS THE EASTERN CARIBBEAN EXTENDING FROM THE
VIRGIN ISLANDS TO WESTERN VENEZUELA. STRONG UPPER LEVEL AND DRY
AIR MASS IS NOW NOTED OVER HISPANIOLA AND PUERTO RICO LIMITING
THE DEVELOPMENT OF SHOWER AND TSTM ACTIVITY.

ATLANTIC OCEAN...                                              A

A RIDGE/TROUGH/RIDGE/TROUGH PATTERN DOMINATES THE DISCUSSION
AREA. AN UPPER LOW LOCATED NEAR 21.5N63W SUPPORTS A 1012 MB
SURFACE LOW PRES CENTERED NEAR 23N67W. SCATTEROMETER DATA SHOW
VERY WELL THE CYCLONIC CIRCULATION ASSOCIATED WITH THIS LOW WITH
THE STRONGEST WINDS OF 20-25 KT WITHIN 240 NM N SEMICIRCLE OF
LOW CENTER. IN ADDITION...VISIBLE SATELLITE IMAGERY REVEALS A
WELL DEFINED SWIRL OF LOW CLOUDS IN ASSOCIATION WITH THIS
FEATURE. MOST OF THE SHOWER AND TSTM ACTIVITY IS DISPLACED TO
THE EAST AND NEAR THE UPPER LEVEL CENTER COVERING FROM 20N TO
23N BETWEEN 59W AND 63W. ENVIRONMENTAL CONDITIONS...ESPECIALLY
THE VERTICAL SHEAR...DO NOT APPEAR TO BE CONDUCIVE FOR TROPICAL
DEVELOPMENT. THE SURFACE LOW IS FORECAST TO DRIFT WESTWARD AND
WEAKEN INTO A TROUGH NEAR THE SE BAHAMAS MON AFTERNOON. THE
TROUGH WILL MERGE WITH A COLD FRONT FORECAST TO MOVE INTO THE NW
WATERS OF THE FORECAST AREA THIS AFTERNOON. THE FRONT WILL
EXTEND FROM 31N75W TO THE FLORIDA STRAITS MON. CURRENTLY...
PRESSURE GRADIENT BETWEEN THE SURFACE LOW AND A RIDGE EXTENDING
FROM BERMUDA TO SOUTH FLORIDA IS PRODUCING A LARGE AREA OF
MAINLY FRESH WINDS ACROSS PARTS OF THE CENTRAL AND WESTERN ATLC.
THE CENTRAL ATLC IS DOMINATED BY BROAD SURFACE RIDGING SUPPORTED
BY AN UPPER LEVEL RIDGE ALONG 46W/47W. AN UPPER LEVEL TROUGH
COVERS THE EASTERN ATLANTIC CENTERED AROUND AN UPPER LOW LOCATED
JUST SOUTH OF THE AZORES. THE UPPER TROUGH SUPPORTS A SURFACE
TROUGH THAT NOW EXTENDS FROM 31N33W TO 28N25W. SCATTERED SHOWERS
AND TSTMS ARE NOTED MAINLY ON THE NORTH SIDE OF THE TROUGH. THE
1202 UTC ASCAT PASS SHOWS THE WIND SHIFT ASSOCIATED WITH THIS
TROUGH WITH THE STRONGEST WINDS OF 20-25 KT JUST N OF 31N. A
TROPICAL WAVE-LIKE HAS MOVED OUT OF AFRICA. A SURFACE TROUGH IS
ANALYZED ALONG 17W FROM 2N TO 9N ON THE 1200 UTC SURFACE MAP.
SCATTERED MODERATE TO ISOLATED STRONG CONVECTION WAS NOTED THIS
MORNING IN ASSOCIATION WITH THIS SYSTEM...BUT CONVECTION IS NOW
DIMINISHING. AN AREA OF SAHARAN DUST IS OBSERVED ON VIS AND
SAHARAN AIR LAYER SATELLITE IMAGERY REACHING 55W. THE REMNANTS
OF A SHEAR AXIS IS STILL EVIDENT ON THE SAME SATELLITE IMAGERY
ACROSS THE TROPICAL ATLC JUST N OF THE AREA OF SAHARAN DUST.

FOR ADDITIONAL INFORMATION PLEASE VISIT
HTTP://WWW.HURRICANES.GOV/MARINE

AT THE REQUEST OF METEO-FRANCE AND THE METEOROLOGICAL SERVICES OF
HAITI AND THE DOMINICAN REPUBLIC...THE TROPICAL ANALYSIS AND
FORECAST BRANCH (TAFB) WILL BEGIN PROVIDING...ON A TEMPORARY
BASIS...A SEPARATE DETAILED SECTION WITHIN THE ATLANTIC TROPICAL
WEATHER DISCUSSION (TWDAT). IT WILL COVER BOTH HAITI AND THE
DOMINICAN REPUBLIC DUE TO THE SHARED GEOGRAPHY OF BOTH COUNTRIES
ON THE ISLAND OF HISPANIOLA.

THE SECTION BEGINS ON MAY 15 2013 AT 1800 UTC...2 PM EDT. IT
WILL PROVIDE GUIDANCE FOR SIGNIFICANT WEATHER EVENTS THAT ARE
EXPECTED TO IMPACT THE REGION THROUGH 48 HOURS...WITH THE FOCUS
ON ASSESSING THE POTENTIAL FOR HEAVY RAINFALL.

$$
FORMOSA


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