[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 201746
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT THU MAR 20 2008

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...THE GULF OF MEXICO...THE CARIBBEAN SEA...NORTHERN
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...METEOROLOGICAL
ANALYSIS...WEATHER OBSERVATIONS...AND RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...THE ITCZ...

FROM THE LIBERIA COAST NEAR 6N10W TO 2N20W CROSSING THE EQUATOR
AT 30W TO 1.5S44W 1N30W. ISOLATED TO SCATTERED MODERATE
CONVECTION FROM 5S TO 3N BETWEEN 2W AND 20W.

...DISCUSSION...

THE GULF OF MEXICO...
A SHORTWAVE TROUGH NEARING 80W OVER THE ERN CONUS IS PUSHING AN
ASSOCIATED COLD FRONT DOWN THE FLORIDA PENINSULA AND THROUGH THE
SERN GULF OF MEXICO/YUCATAN...EXTENDING FROM NEAR NAPLES FL TO
22N88W AND THEN SOUTHWARD TO 15N91W AT 1500 UTC.  VISIBLE
SATELLITE IMAGERY REVEALS A BROAD BAND OF LOW- TO MID-LEVEL
CLOUDS NEAR AND WITHIN ABOUT 150 NM WEST OF THE BOUNDARY
...THOUGH WITH LITTLE TO NO DEEP CONVECTION. HOWEVER...THE
COMBINATION OF 1.5 TO 1.75 PRECIPITABLE WATER VALUES...DYNAMICS
ASSOCIATED WITH THE TAIL OF A 90-130 KT NE-SW JET EXTENDING
INTO THE NERN GULF OF MEXICO...AND SUFFICIENT LIFT ALONG THE
FRONT COULD STILL IGNITE SCATTERED SHOWERS AND TSTMS NEAR AND
AHEAD OF THE BOUNDARY LATER THIS AFTERNOON AND EVENING. IN
ADDITION
...A MORNING QUIKSCAT PASS INDICATED A MOSTLY N-NE LOW-LEVEL
FLOW OF 15-20 KT WEST OF 90W AND N OF THE FRONT...WITH SOME
OCCASIONAL 25 KT WINDS POSSIBLE CLOSE TO THE MOUTH OF THE MS
RIVER. SPOTTY SHIP REPORTS AND BUOY OBSERVATIONS SUGGEST A
SIMILAR NLY FLOW E OF 90W AND DIRECTLY BEHIND THE FRONT...WITH
WINDS LIKELY TO VEER MORE N TO NE BY LATE TODAY.  AS A RESULT OF
THE GALE FORCE WINDS FROM YESTERDAY...SEAS ARE STILL AROUND 6 TO
10 FT IN NLY SWELL WEST OF 85W EXCEPT OFFSHORE THE TX COAST.
BEHIND THE FRONT OVER THE ISTHMUS OF TEHUANTEPEC...A SLIGHTLY
LATER QUIKSCAT PASS REVEALED 45 KT WINDS JUST SOUTH OF THE GULF
OF TEHUANTEPEC...WITH WINDS LIKELY TO DIMINISH BELOW GALE FORCE
BY FRI AFTERNOON.


AS THE ERN CONUS SHORTWAVE HEADS EAST TONIGHT AND FAILS TO DIG
APPRECIABLY...EXPECT THE COLD FRONT TO CLEAR THE FLORIDA
PENINSULA AND BECOME STATIONARY FROM THE FL STRAITS TO NORTH OF
THE YUCATAN FRI MORNING...WITH A 1028MB SURFACE RIDGE BEHIND IT
OVER THE CAROLINAS.  THIS PATTERN SHOULD FAVOR A BRISK ELY FLOW
E OF 90W MUCH OF FRI...WHICH SHOULD KEEP ALL BUT THE NW GULF
WITH 5 TO 8 FT SEAS IN NE TO E SWELL.  LATER FRI...WEAK
SHORTWAVE ENERGY PASSING THROUGH THE DEEP SOUTH AND GULF OF
MEXICO SHOULD ACTIVATE A WEAK SURFACE WAVE ALONG THE STATIONARY
BOUNDARY OVER THE SOUTH CENTRAL GULF...WHICH SHOULD TRACK
RAPIDLY ENE ACROSS CENTRAL FL SAT. SOON THEREAFTER...AN EVEN
STRONGER NRN STREAM DISTURBANCE SHOULD DRIVE A STRONGER FRONT
OFF THE SERN CONUS COAST SUN MORNING...WITH STRONG HIGH PRESSURE
BUILDING INTO THE GULF BEHIND BOTH SYSTEMS.

CARIBBEAN SEA...

THE TAIL OF A COLD FRONT ASSOCIATED WITH WHAT ONCE WAS A STRONG
STORM CENTER OVER THE WESTERN ATLANTIC EARLIER THIS WEEK HAS
PUSHED WELL INTO THE EASTERN CARIBBEAN AND LESSER ANTILLES AS OF
THIS MORNING.  VISIBLE SATELLITE IMAGERY SHOWS PATCHES OF
STRATOCUMULUS CLOUDS HAVING PENETRATED FROM ANTIGUA THROUGH
PUERTO RICO...THOUGH THEIR COVERAGE HAS DIMINISHED CONSIDERABLY
SINCE 1200 UTC. UPPER-AIR DATA FROM SAN JUAN ALSO INDICATES A
RECOVERY TO THE NORMAL TRADE WIND INVERSION ACROSS THE
REGION...THOUGH THE INVERSION LEVEL OF 750 MB IS STILL LIKELY
MUCH HIGHER-THAN-AVERAGE. IN ADDITION...SURFACE OBS ACROSS THE
REGION INDICATE DEWPOINTS FROM THE UPPER 50'S TO MID 60'S OVER
THE NE CARIBBEAN NORTH OF THE DIFFUSE BOUNDARY...WITH
TEMPERATURES STILL SEVERAL DEGREES COOLER THAN CLIMATOLOGICAL
AVERAGES.

ELSEWHERE...STRONG HIGH PRESSURE BEHIND THE FRONT HAS LOST MUCH
OF ITS VIGOR THE LAST TWO DAYS...AND THUS THE TRADE WIND FLOW
OVER TH ERN AND CENTRAL CARIBBEAN HAS DRASTICALLY DIMINISHED.
HOWEVER...A 1038 UTC QUIKSCAT PASS DID SHOW A HEALTHY AREA OF
20 TO 25 KT WINDS BETWEEN 70W AND 78W...WITH SEVERAL INDICATIONS
OF 30 KT WINDS DIRECTLY OFFSHORE THE COAST OF COLOMBIA.  SEAS
CONTINUE TO REMAIN 6 TO 12 FT IN MOSTLY NE TO E SWELL.  HOWEVER
...LARGE LONG PERIOD SWELL ORIGINATING FROM THE EARLY WEEK
STORM OVER THE WRN ATLANTIC CONTINUES TO PROPAGATE THROUGH THE
ATLANTIC PASSAGES...CREATING SEAS OF 12 TO 17 FT THROUGH PUERTO
RICO AND PARTS OF THE NORTHERN ANTILLES.  OTHERWISE...SEVERAL
STREAMERS OF CLOUDS AND SHOWERS ARE FORMING DOWNWIND OF THE
LARGE ISLANDS IN THE ANTILLES CHAIN...WITH A MORE PROMINENT
BROKEN BAND EXTENDING ALONG 17N63W 16N68W 16N73W.

FINALLY...AN ANOMALOUSLY STRONG MID- TO UPPER-LEVEL ANTICYCLONE
COVERS MUCH OF THE BASIN TODAY WITH A CONTINUATION OF STRONG
SUBSIDENCE SEEN IN WATER VAPOR IMAGERY ALL AREAS E OF 85W.  AS A
RESULT OF THE UNUSUALLY STRONG RIDGE ALOFT...DEEP EASTERLY FLOW
AT UPPER-LEVELS COVER MUCH OF SOUTH AMERICA INTO THE ERN
PACIFIC...AN UNUSUAL SIGHT FOR THE THIRD WEEK OF MARCH. OVER THE
NEXT FEW DAYS...MODEL GUIDANCE INDICATES THAT THIS RIDGE SHOULD
BEGIN TO SHIFT FARTHER EAST...AS HEIGHTS FALL OVER THE GULF OF
MEXICO AND ERN CONUS COAST LATE THIS WEEKEND.

ATLANTIC...
THE SAME COLD FRONT PUSHING THROUGH THE SERN GULF OF MEXICO THIS
MORNING IS ALSO MAKING SEWD PROGRESS OVER THE SW ATLC...
EXTENDING ALONG 31N77W TO AROUND VERO BEACH FL AT 1500 UTC. AN
EARLIER QUIKSCAT PASS SHOWED A BROAD AREA OF SWLY 25- TO 30-KT
WINDS WITHIN ABOUT 400 NM EAST OF THE FRONT NORTH OF 28...WHICH
IS GENERATING 10 TO 13 FT SEAS IN MIXED NE AND SW SWELL AHEAD OF
THE FRONT.  SATELLITE IMAGERY ALSO INDICATES A THIN LINE OF
BROKEN SHOWERS AND TSTMS FORMING WITHIN ABOUT 60 NM EAST OF THE
FRONT FROM ACROSS SOUTH FLORIDA WITH A MORE CONCENTRATED LINE
FARTHER NE.  EXPECT THE FRONT TO CONTINUE SWD TODAY...SETTLING
INTO NORTH CENTRAL BAHAMAS AND STALLING OUT BY LATE FRI...WITH A
1025MB SFC RIDGE MOVING OFFSHORE THE SE CONUS COAST.

LONG PERIOD N TO NE SWELL CONTINUES TO DOMINATE MUCH OF THE
ATLANTIC BASIN SOUTH OF 31N...REMNANT FROM THE STORM SYSTEM
WHICH AFFECTED THE WRN ATLANTIC EARLY THIS WEEK.  SHIP REPORTS
AND BUOY OBSERVATIONS CONTINUE TO SHOW 10 TO 15 FT SEAS IN NE
SWELL WEST OF 65W...WITH 16 TO 22 FT SEAS IN NW TO N SWELL NORTH
OF 20N AND EAST OF 60W. THE SWELL HAS PROPAGATED DEEP INTO THE
TROPICAL ATLANTIC...STRAIGHT TO THE SOUTH AMERICAN COAST AND
SHOULD CONTINUE DOING SO THROUGH THE WEEKEND...WITH SEAS
GRADUALLY SUBSIDING FROM NW TO SE.

ELSEWHERE...A LARGE CLOSED CYCLONE NEAR 36N49W REMAINS NEARLY
STATIONARY...BLOCKED BY AN ENORMOUS BLOCKING HIGH OVER THE FAR
NORTH ATLANTIC SOUTH OF GREENLAND.  AN ASSOCIATED COLD FRONT
EXTENDS ALONG 31N41W TO 15N51W AND IS SLOWLY PRESSING SEWD.
AS THE BLOCK WEAKENS THE NEXT FEW DAYS...EXPECT THE CLOSED
CYCLONE TO GRADUALLY HEAD EWD ALONG WITH THE COLD WHICH SHOULD
PUSH EAST OF THE AREA BY EARLY SAT MORNING.

OTHERWISE...A FLAT ANTICYCLONE AT MID- TO UPPER-LEVELS COVERS
THE TROPICAL ATLANTIC...WITH AN AXIS ALONG 15N.  ANOMALOUS ELY
FLOW CONTINUES SOUTH OF 10N FROM THE LESSER ANTILLES EWD TO THE
COAST OF AFRICA.


$$
KIMBERLAIN




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