[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 050555
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT SAT APR 05 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0430 UTC.

...THE ITCZ...

ITCZ AXIS IS CENTERED ALONG 6N11W 3N20W 1N30W CROSSING THE
EQUATOR AT 40W TO 1S45W. SCATTERED STRONG CONVECTION WITHIN 300
NM EITHER SIDE OF AXIS BETWEEN 24W AND 33W. SCATTERED MODERATE
FROM EQUATOR TO 2N BETWEEN 44W AND 48W.

...DISCUSSION...

GULF OF MEXICO...

A SOUTHERN STREAM SHORTWAVE TROUGH PASSING THROUGH THE SOUTHERN
PLAINS IS RESPONSIBLE FOR A WEAK COLD FRONT ENTERING THE NW GULF
OF MEXICO AND FAR NE MEXICO. ALTHOUGH AN EARLIER QUIKSCAT PASS
REVEALED NE 20- TO 25-KT WINDS BEHIND THE FRONT...MUCH OF THE
DATA APPEARED TO BE RAIN-CONTAMINATED AND THUS NOT CONSIDERED
RELIABLE.  HOWEVER...A COMBINATION OF COASTAL...CMAN...AND BUOY
OBSERVATIONS DO CONFIRM N TO NE WINDS OF 20 TO POSSIBLY 25 KT
DIRECTLY BEHIND THE FRONT. RADAR AND SATELLITE IMAGERY SHOWS
SCATTERED TO LOCALLY NUMEROUS TSTMS WITHIN 90 NM NW OF THE FRONT
IMMEDIATELY OFFSHORE THE UPPER TX AND SW LA COASTS...N OF WHAT
COULD BE A WEAK 1007 MB SFC LOW ANALYZED NEAR 29N93W. ELSEWHERE
E OF THE FRONT...SE TO S WINDS OF 15 TO 20 KT COVER THE GULF...
WITH SKIES REMAIN MOSTLY CLOUD FREE EXCEPT FOR SOME ISOLATED
CONVECTIVE CELLS SPROUTING UP OVER THE FAR NE.

SHORT-TERM MODEL GUIDANCE SHOWS THE SOUTHERN PLAINS SHORTWAVE
BEGINNING TO LIFT OUT OVER THE SE U.S. LATE SAT...UNABLE TO DIG
MUCH FURTHER THANKS TO A FAIRLY SOLID MID-LEVEL RIDGE OVER THE
WESTERN ATLANTIC.  DESPITE THIS...A BROAD PATTERN OF UPPER-LEVEL
DIVERGENCE...WARM AIR ADVECTION...AND POSITIVE VORTICITY
ADVECTION AHEAD OF THE SYSTEM SHOULD RESULT IN FAIRLY WIDESPREAD
CONVECTIVE RAINS NOT ONLY OVER THE SOUTHERN TIER AND GULF COAST
BUT ALSO OVER THE NORTHERN GULF WATERS THROUGH MUCH OF SAT.
HOWEVER...WITH THE UPPER SUPPORT ALREADY PUSHING NE AND THE MID-
TO UPPER-LEVEL BECOMING NEARLY PARALLEL ALONG THE FRONT...EXPECT
THE FRONT TO STALL NEARLY HALFWAY ACROSS THE GULF WITH A NE-SW
ORIENTATION. WHAT IS LEFT OF THE FRONT SHOULD RETREAT AS A WARM
FRONT SUN INTO MON...LYING CLOSE TO OR JUST INLAND FROM THE GULF
COAST.

CARIBBEAN SEA...

WATER VAPOR IMAGERY REVEALS HIGH-LEVEL WESTERLY FLOW DOMINATING
MUCH OF THE BASIN...WITH A WEAK MID- TO UPPER-LEVEL TROUGH
EXTENDING FROM 21N79W INTO THE E PACIFIC W OF COSTA RICA.
MODERATE TO STRONG SUBSIDENCE ASSOCIATED WITH A LARGE MID- TO
UPPER-LEVEL ANTICYCLONE IN THE TROPICAL E PACIFIC IS OBSERVED AS
FAR E AS THE WESTERN CARIBBEAN W OF THE TROUGH AXIS. HOWEVER...A
PLUME OF MOISTURE WITH ORIGINS FROM THE AMAZON IS BEING DRAWN
NORTHWARD OVER THE CENTRAL CARIBBEAN E OF THE TROUGH AXIS. THIS
SUBTLE INCREASE IN UPPER TROPOSPHERIC MOISTURE AND THE DIFFLUENT
UPPER-LEVEL FLOW HAS HELPED TO EXCITE SOME CONVECTION...ALTHOUGH
WHAT HAS FORMED IS PRETTY SCARCE. IN FACT...ONLY SPORADIC
CONVECTIVE ELEMENTS ARE NOTED FROM PANAMA THROUGH NORTHERN
COLOMBIA...ALL OF WHICH ARE GRADUALLY DIMINISHING. SCATTERED
LATE AFTERNOON CONVECTION...LIKELY A RESULT OF LOCAL SEA BREEZE
CIRCULATIONS ...ALSO CONTINUES TO WIND DOWN OVER CUBA.

OTHERWISE...STRONG HIGH PRESSURE OVER THE CENTRAL ATLANTIC HAS
AN EXTENSION INTO THE CARIBBEAN SEA AND IS PROVIDING FRESH
TRADES ACROSS THE EASTERN AND PARTS OF THE CENTRAL PART OF THE
AREA. HOWEVER...REAL-TIME NCEP RE-ANALYSIS DATA INDICATES THAT
CURRENT TRADES ARE FAIRLY CHARACTERISTIC OF THIS TIME OF THE
YEAR...EXCEPT PERHAPS SLIGHTLY STRONGER-THAN-NORMAL OVER THE FAR
E.

OVER THE NEXT FEW DAYS...A WELL-DEFINED MID- TO UPPER-LEVEL
RIDGE SHOULD SET UP SHOP N OF THE CARIBBEAN...IN THE VICINITY OF
25N62W...WHILE THE TROUGH CURRENTLY OVER THE WESTERN CARIBBEAN
MOVES W AND LOSES ITS IDENTITY. THIS SHOULD SET UP A PATTERN OF
LIGHT UPPER-LEVEL WINDS ACROSS THE AREA...WITH SUBSTANTIAL
EASTERLY WIND ANOMALIES LIKELY FROM THIS WEEKEND INTO EARLY NEXT
WEEK.  MEANWHILE...THE STRONG SURFACE RIDGE NOW NEAR 36N54W
SHOULD WEAKEN AND SHIFT SE TO 28N62W BY EARLY MON...WHICH SHOULD
ALLOW TRADES TO RELAX OVER THE EASTERN AND CENTRAL CARIBBEAN.

ATLANTIC OCEAN...
AN ANOMALOUSLY STRONG MID-LEVEL RIDGE REMAINS LOCKED IN PLACE
OVER THE WESTERN ATLANTIC NEAR 25N62W...DIRECTING THE STRONGER
MID-LATITUDE FLOW OVER THE EASTERN CONUS N OF THE AREA. MUCH OF
THE STRONGER MID-LATITUDE FLOW DIGS EASTWARD INTO A BROAD MID-
TO UPPER-LEVEL TROUGH W OF 50W AND N OF 15N...WITH AN ASSOCIATED
DEEP-LAYERED CYCLONIC CIRCULATION CLOSE TO 39N36W.  W OF THE
TROUGH...A LARGE DOME OF SURFACE HIGH PRESSURE IS CENTERED NEAR
36N54W AND DOMINATES MUCH OF THE ATLANTIC...IN SOME CASES WITH
ENHANCED TRADES. IN FACT...AN EARLIER QUIKSCAT PASS REVEALED NE
TO E WINDS OF 20- TO 25-KT OVER A LARGE EXPANSE S OF 20N AND E
OF THE LESSER ANTILLES TO ABOUT 40W....WITH SEAS GENERALLY 10 TO
13 FT IN NE SWELL. THE ABOVE PATTERN SHOULD CONTINUE INTO THE
WEEKEND...WITH THE TRADES SLOWLY DIMINISHING TO CLIMATOLOGICAL
LEVELS AND SEA GRADUALLY SUBSIDING.

W OF 50W...A BROAD SURFACE CYCLONIC FLOW COVERS THE AREA N OF
25N...WITH A SURFACE COLD FRONT LOCATED FROM 31N38W TO 28N46W TO
30N56W.  THE FRONT IS MARKED BY THE LEADING EDGE OF A FAIRLY
DENSE STRATOCUMULUS DECK OF CLOUDS...THOUGH THERE IS LITTLE ELSE
ALONG THE IMMEDIATE FRONT.  AS THE FRONT RACES SE SAT...THE
INJECTION OF COOLER AIR SHOULD BRIEFLY RE-INVIGORATE THE LARGE
CYCLONIC CENTER NEAR THE SE AZORES...WHICH SHOULD REINFORCE THE
CYCLONIC FLOW OVER THE NE PART OF THE AREA.

ELSEWHERE...WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS INDICATE
A NARROW RIDGE S OF ABOUT 12N FROM THE NW COAST OF AFRICA TO
JUST SE OF THE ANTILLES. THE DEEP EASTERLIES S OF THE RIDGE AXIS
HAVE BEEN PROVIDING A FAVORABLE ENVIRONMENT FOR ENHANCED
CONVECTION ALONG THE ITCZ THE LAST FEW DAYS...AND THIS PATTERN
OF ANOMALOUS EASTERLY FLOW SHOULD CONTINUE FOR THE NEXT FEW DAYS.

$$
KIMBERLAIN


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