[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 292329
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
705 PM EST TUE FEB 28 2012

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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2300 UTC.

...THE ITCZ/THE MONSOON TROUGH...

THE MONSOON TROUGH EXTENDS ACROSS W AFRICA TO THE COAST OF
LIBERIA NEAR 06N10W TO 3N20W...WHERE IT TRANSITIONS TO ITCZ...
CONTINUING W-SW...AND CROSSING THE EQUATOR NEAR 35W TO 1S39W AND
BACK ACROSS THE EQUATOR AT 45W ENDING NEAR THE MOUTH OF THE
AMAZON. SCATTERED MODERATE/ISOLATED STRONG CONVECTION IS FROM
2.5S-1.5N BETWEEN 30W AND 45W. SIMILAR ACTIVITY IS FOUND WITHIN
180 NM S OF THE MONSOON TROUGH E OF 17W.

...DISCUSSION...

THE GULF OF MEXICO...
A STRONG UPPER LEVEL RIDGE CONTINUES TO DOMINATE THE GULF OF
MEXICO THIS AFTERNOON...ANCHORED ON AN UPPER ANTICYCLONE OVER
THE TROPICAL EPAC NEAR 08N96W. RIDGE AXIS EXTENDS N-NE ACROSS SE
MEXICO AND THROUGH THE CENTRAL LOUISIANA COAST...BUT HAS
WEAKENED N OF 33N DUE TO SHORTWAVE ENERGY MOVING INTO THE GREAT
LAKES REGION. ASSOCIATED SUBSIDENCE AND STABLE MIDDLE TO UPPER
LEVEL CONDITIONS PREVAIL ACROSS THE BASIN E OF 95W. A COLD
FRONTAL SYSTEM SUPPORTED BY A DEEP LAYERED CYCLONE EMBEDDED
WITHIN THE GREAT LAKES SHORTWAVE RUNS THROUGH THE MISSISSIPPI
RIVER VALLEY...ACROSS THE NW CORNER OF LOUISIANA AND CONTINUES
SW ACROSS E AND SE TEXAS. THE UPPER RIDGE IS EXPECTED TO REMAIN
IN PLACE THROUGH FRI AND ACT TO BLOCK THIS FRONT FROM REACHING
THE TEXAS COAST TONIGHT. AT THE SURFACE...A 1026 MB HIGH
CENTERED OVER THE W ATLC JUST NE OF BERMUDA EXTENDS A RIDGE SW
ACROSS FLORIDA AND THEN W-SW ACROSS THE GULF...YIELDING SLY
RETURN FLOW IN ADVANCE OF THE MS VALLEY COLD FRONT. MODERATE SE
TO S WINDS GENERALLY PREVAIL ACROSS THE GULF THIS AFTERNOON...
AND HAVE DECREASED SLIGHTLY IN THE PAST FEW HOURS AS THE FRONT
HAS HAS MOVED CLOSER. LOW STRATUS AND FOG ACROSS N FLORIDA AND
EXTREME NE PORTIONS OF THE GULF HAS BURNED OFF THIS AFTERNOON...
EXCEPT FOR A VERY SMALL AREA LINGERING OVER THE BIG BEND REGION.
OTHERWISE...MOSTLY CLEAR TO PARTLY CLOUDY SKIES PREVAIL ACROSS
MOST OF THE GULF THIS AFTERNOON. MODEST SURFACE RIDGING IS
EXPECTED TO PERSIST IN PLACE THROUGH FRI NIGHT BEFORE THE NEXT
COLD FRONT ENTERS THE NW WATERS SAT MORNING.

THE CARIBBEAN SEA...
CONFLUENT FLOW ALOFT IS PRODUCING A BROAD ZONE OF STRONG
SUBSIDENCE ACROSS ALL BUT THE NE CARIBBEAN...WITH WATER VAPOR
IMAGERY SHOWING CLEAR SKIES INTO THE LOWER LEVELS ACROSS THE
AREA S OF JAMAICA. DOWNSTREAM OF THE GULF OF MEXICO RIDGE...A
SHORTWAVE ACROSS THE SW N ATLC WAS BETWEEN 65W AND 72W WITH AN
EMBEDDED MID TO UPPER CYCLONE NEAR 25N68W. STRONG CYCLONIC
TURNING S AND SE OF THIS CYCLONE WAS ACTING TO ENHANCE DIURNAL
CONVECTION ACROSS HISPANIOLA AND PUERTO RICO THIS AFTERNOON...
WITH THE LIGHTNING DETECTION NETWORK STILL SHOWING STRIKES ATTM.
AT THE SURFACE...THE MODEST ATLC HIGH PRESSURE RIDGE CONTINUES
TO PRODUCE MODERATE TO FRESH TRADEWINDS ACROSS THE CARIBBEAN E
OF 80W...WITH SUFFICIENT PRES GRADIENT TO MAINTAIN MINIMAL GALES
OFF THE COAST OF COLOMBIA. SEVERAL AREAS OF PATCHY LOW LEVEL
MOISTURE EMBEDDED IN THE TRADES COULD BE SEEN IN SATELLITE
IMAGERY THIS AFTERNOON MOVING WWD ACROSS THE BASIN...PRODUCING
AREAS OF SCATTERED QUICKLY PASSING SHOWERS. AMPLE MOISTURE
ACROSS W PORTIONS OF THE BASIN CONTINUES TO YIELD SCATTERED TO
NUMEROUS SHOWERS ACROSS UPSLOPE PORTIONS OF CENTRAL AMERICA.
LITTLE CHANGE IS EXPECTED IN THIS PATTERN DURING THE NEXT 24
HOURS.

THE ATLANTIC OCEAN...
THE SHORTWAVE MENTIONED ABOVE ACROSS THE SW N ATLC WAS EMBEDDED
WITHIN A LARGER AND BROAD UPPER LEVEL TROUGH EXTENDING FROM THE
N ATLC S THEN SW THROUGH THE SHORTWAVE AND CONTINUING SW TO THE
W CENTRAL CARIB. E OF THIS BROAD TROUGH...UPPER LEVEL WLY FLOW
PREVAILED...WITH AN EMBEDDED SHORTWAVE ALONG ABOUT 30W AND N OF
15N. S OF THIS...AN UPPER LEVEL RIDGE EXTENDED E TO W ACROSS THE
DEEP TROPICS ALONG 08-09N...FROM CENTRAL AFRICA TO NRN S
AMERICA. UNSTABLE ATMOSPHERIC CONDITIONS ARE FOUND SE AND S OF
BOTH OF THE SHORTWAVES MOVING ACROSS THE BASIN. THE PARENT
CYCLONE ASSOCIATED WITH THE BROAD UPPER TROUGH ACROSS THE ATLC
SUPPORTS A COLD FRONT THAT STRETCHES FROM THE CENTRAL ATLC TO
NEAR 31N70W. THIS FRONT WILL SINK SLOWLY SE INTO N PORTIONS OF
THE AREA AND WEAKEN DURING THE NEXT 24 HOURS. FARTHER E...AN OLD
COLD FRONT EXTENDED FROM JUST N OF THE AZORES WWD TO NEAR 29N33W
AND WAS ALSO WEAKENING...AND LIKELY TO BECOME A SHEARLINE DURING
THE NEXT 24 HOURS. REMNANT MOISTURE ASSOCIATED WITH A DISSIPATED
COLD FRONT OF THE PAST SEVERAL DAYS STRETCHED E TO W FROM 50W TO
70W ALONG ABOUT 25N...AND WAS INTERACTING WITH A JET DYNAMICS
ASSOCIATED WITH THE BROAD UPPER TROUGH TO PRODUCE TWO DISTINCT
AREAS OF SCATTERED MODERATE TO STRONG CONVECTION. WIND SHEAR
ASSOCIATED WITH THE UPPER TROUGH HAS INCREASED AND BECOME
EXCESSIVE LATE THIS AFTERNOON...AND CONVECTION HAS THUS
DIMINISHED. OTHERWISE...HIGH PRESSURE AND MODERATE TO FRESH
TRADEWINDS DOMINATE THE REMAINDER OF THE BASIN...WITH 20-25 KT
NE TRADES FOUND FROM 10N TO 20N E OF 60W...AND MODERATE E TO SE
FLOW W OF 60W. AN ELONGATED PLUME OF SAL AND VERY STABLE LOW TO
MIDDLE LEVEL AIR EXTENDS FROM WRN AFRICA NEAR 12N...W-SW ACROSS
THE DEEP TROPICS TO BEYOND 06N50W...WHERE IT HAS BEGUN TO
INTERACT WITH ITCZ CONVECTION ALONG NE COASTAL SECTIONS OF S
AMERICA...WITH THE ASSOCIATED LLVL WIND SURGE ALONG THE LEADING
EDGE OF THE SAL FORCING DIURNAL CONVECTION ACROSS S AMERICA WELL
INLAND TO NEAR 60W. FARTHER E...CONVECTION IS VERY ACTIVE S OF
THE MONSOON TROUGH...AND ACROSS THE GULF OF GUINEA WWD TO 17W. A
MID TROPOSPHERIC JET HAS BECOME ESTABLISHED ACROSS THIS
REGION...AND S OF THE MONSOON TROUGH WHERE AMPLE TROPICAL
MOISTURE RESIDES. THIS HAS CREATED AN ENVIRONMENT CONDUCIVE FOR
BAROTROPIC GROWTH FROM THE JET...AND AN EQUATORIAL ELY WAVE
APPEARS TO HAVE FORMED ALONG ABOUT 07W THERE. GFS FORECASTS
SUGGESTS THIS WAVE WILL MOVE WWD AND QUICKLY BEGIN TO WEAKEN IN
ABOUT 36 HOURS.

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

$$
STRIPLING





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