[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 051058
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1045 UTC.

...THE ITCZ...

ITCZ AXIS IS CENTERED ALONG 7N11W 6N17W 2N22W CROSSING THE
EQUATOR AT 31W TO 5S37W. SCATTERED TO WIDESPREAD STRONG
CONVECTION
WITHIN 300 NM EITHER SIDE OF AXIS BETWEEN 22W AND 31W. ISOLATED
MODERATE FROM 3S TO 5N BETWEEN 40W AND 48W.

...DISCUSSION...

GULF OF MEXICO...
A SOUTHERN STREAM SHORTWAVE TROUGH PASSING THROUGH THE ARKLATEX
REGION IS DRAGGING A WEAK COLD FRONT INTO THE NW GULF OF MEXICO
AND FAR NE MEXICO. ALTHOUGH A QUIKSCAT PASS FROM YESTERDAY
EVENING REVEALED N TO 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 IN THAT RANGE
DIRECTLY BEHIND THE FRONT...WITH SEAS BUILDING TO 5 TO 7
FT...AND A SOLID DECK OF STRATUS CLOUDS EXTENDING BACK ALMOST
150 NM. RADAR AND SATELLITE IMAGERY SHOW SCATTERED TO LOCALLY
NUMEROUS TSTMS WITHIN 30 TO 60 NM E OF THE FRONT FROM THE SE LA
COAST NE INTO THE WESTERN FL PANHANDLE.  A CLOSER INSPECTION OF
THESE OBSERVATIONS REVEALS A WELL-DEFINED OUTFLOW BOUNDARY
PROPAGATING SE FROM THIS NASCENT CONVECTIVE LINE...WHILE
INDIVIDUAL CELLS CONTINUE MOVING NE AT 30 TO 40 KT. IN
ADDITION...SEVERAL OBSERVATIONS ALSO SUGGEST A WEAK 1007 MB SFC
LOW IN ITS FORMATIVE STAGES ALONG THE FRONT ANALYZED CLOSE TO
30N91W ...MOVING NE AT 20 TO 25 KT. ELSEWHERE SE 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 FROM 26N TO 27N BETWEEN 90W AND 92W AND AHEAD OF
THE WITHIN ABOUT 60 NM SE OF THE SE TIP OF LA.

SHORT-TERM MODEL GUIDANCE SHOWS THE ARKLATEX 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 ACROSS THE INTERIOR SE BUT ALSO ALONG
THE N CENTRAL AND NE GULF COAST TODAY. 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 WEAKENING 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 IGNITE SOME CONVECTION LATE
YESTERDAY...ALTHOUGH WHAT FORMED WAS PRETTY SCARCE. IN FACT...
ONLY SPORADIC CONVECTIVE ELEMENTS WERE NOTED FROM PANAMA THROUGH
NORTHERN COLOMBIA...WITH UNRELATED LATE AFTERNOON CONVECTION...
OVER CUBA...LIKELY A RESULT OF LOCAL SEA BREEZE CIRCULATIONS. AT
THIS HOUR...WHAT REMAINS IS SOME ISOLATED CONVECTIVE CELLS
IMMEDIATELY SE OF THE SE NICARAGUAN COAST.

OTHERWISE...STRONG SURFACE 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 40N36W.  W OF THE
TROUGH...A LARGE DOME OF SURFACE HIGH PRESSURE IS CENTERED NEAR
34N51W AND DOMINATES MUCH OF THE ATLANTIC...IN SOME CASES WITH
ENHANCED TRADES. IN FACT...EARLIER QUIKSCAT PASSES AS WELL AS
THE EASTERN EDGE OF A MORE RECENT 0842 UTC REVEAL 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 9 TO 12 FT
IN NE SWELL. THE ABOVE PATTERN SHOULD CONTINUE INTO THE
WEEKEND...WITH THE TRADES GRADUALLY DIMINISHING TO
CLIMATOLOGICAL LEVELS AND SEA SUBSIDING TO 7 TO 10 FT BY LATE
SUN.

W OF 50W...A BROAD SURFACE CYCLONIC FLOW COVERS THE AREA N OF
25N...WITH A SURFACE COLD FRONT LOCATED FROM 31N31W TO 26N44W TO
THE BEGINNING A WARM FRONT STARTING AT 31N56W. 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 TODAY...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
ALONG WITH THE PRESENCE OF A KELVIN WAVE APPROACHING 10W HAVE
BEEN PROVIDING A FAVORABLE ENVIRONMENT FOR ENHANCED CONVECTION
ALONG THE ITCZ THE LAST FEW DAYS. THIS PATTERN OF ANOMALOUS
EASTERLY FLOW AND ENHANCED CONVECTION SHOULD CONTINUE THROUGH
EARLY THIS WEEKEND BEFORE DIMINISHING AS THE KELVIN WAVE
PROPAGATES E OF THE AREA.

$$
KIMBERLAIN




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