[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 102346
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT THU APR 10 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...ITCZ...
ITCZ AXIS IS CENTERED ALONG 05N09W 4N20W 1N30W 1N50W. SCATTERED
MODERATE AND EMBEDDED STRONG CONVECTION IS TIGHTLY CLUSTERED
WITHIN 150 NM N OF THE AXIS BETWEEN 17W AND 20W. SCATTERED
MODERATE CONVECTION IS WITHIN 150 NM EITHER SIDE OF THE AXIS
BETWEEN 31W-50W.

...DISCUSSION...
GULF OF MEXICO...
A LARGE MID- TO UPPER-LEVEL RIDGE EXTENDS FROM THE FL PENINSULA
SW THROUGH THE BAY OF CAMPECHE AND DOMINATES MOST OF THE REGION
WITH MODERATE TO STRONG SUBSIDENCE...ESPECIALLY S OF 24N E OF
92W. HOWEVER...UPPER TROPOSPHERIC SOUTHWESTERLY FLOW IS ON THE
INCREASE OVER THE NW GULF...AS A STRONG CLOSED CYCLONE AND
ASSOCIATED SHORTWAVE TROUGH MOVE OUT OF THE PLAINS AND INTO THE
MIDWEST. THIS TROUGH IS PROVIDING SUPPORT FOR A COMPLEX 987 MB
LOW PRESSURE SYSTEM OVER THE CENTRAL PLAINS...WITH AN ASSOCIATED
COLD FRONT LOSING ITS IDENTITY AS IT ADVANCES THROUGH THE MS
RIVER VALLEY THROUGH SE TX. THE PRESSURE GRADIENT BETWEEN LOW
PRESSURE ON THE PLAINS AND A 1022 MB SURFACE RIDGE NEAR BERMUDA
IS GENERATING A BRISK SE TO S RETURN FLOW OF 20- TO 25-KT W OF
84W. THE DURATION AND FETCH OF THIS SLY FLOW HAS BEEN FAIRLY
CONSTANT SINCE LAST NIGHT...WHICH HAS HELPED SEAS TO BUILD UP TO
11 FT OVER THE NW WATERS.  OTHERWISE...THE LATEST SURFACE
ANALYSIS INDICATES AN ENE-WSW ORIENTED RIDGE ALONG OR JUST
OFFSHORE THE NORTHERN GULF COAST...WITH AN AXIS EXTENDING FROM
30N85W TO 26N93W. ASIDE FROM A FEW SHALLOW CLOUDS OVER THE EAST
CENTRAL GULF...FAIR WEATHER PREVAILS ACROSS THE REGION...BUT
LOW- TO MID-LEVEL CLOUDS ALONG THE TX AND SW LA COASTS HERALD
THE WEAKENING FRONT APPROACHING THE AREA.

AS THE DEEP TROUGH OVER THE PLAINS HEADS INTO THE EASTERN STATES
FRI...A REINFORCING COLD FRONT SHOULD DIVE FROM THE FRONT RANGE
OF THE ROCKIES TO THE NW GULF COAST.  THE FRONT SHOULD SWEEP
ACROSS THE REMAINDER OF THE AREA SAT AND SUN WITH LITTLE FANFARE
...USHERING IN A BRISK NW TO N WIND OF 20 TO 30 KT...EXCEPT TO
GALE FORCE OVER THE SW GULF AND BAY OF CAMPECHE SUN.  EXPECT
SEAS TO BUILD UP TO 10 TO 15 FT OVER A LARGE PART OF THE GULF
THIS WEEKEND...WITH WINDS AND SEAS GRADUALLY SUBSIDING MON AS
HIGH PRESSURE BUILDS IN FROM THE W.

CARIBBEAN SEA...
A POSITIVELY-TILTED MID- TO UPPER-LEVEL TROUGH IS DIGGING INTO
THE CENTRAL CARIBBEAN...WITH AN AXIS EXTENDING FROM HISPANIOLA
TO N OF SAN ANDRES NICARAGUA. LIKE YESTERDAY...CLOUD-TRACKED
WINDS AND WATER VAPOR IMAGERY SHOW A PLUME OF ENHANCED MID- TO
UPPER-LEVEL MOISTURE SPREADING FROM ACTIVE CONVECTION IN THE E
PACIFIC S OF CENTRAL AMERICA ENE TO THE NE CARIBBEAN AHEAD OF
THE TROUGH. DESPITE THE ENHANCED MOISTURE...LITTLE CONVECTION IS
NOTED...EXCEPT DIRECTLY UNDERNEATH THE TROUGH OVER HISPANIOLA
AND IN ONE LONE STREAMER OVER THE SE CARIBBEAN. STRONGLY
CONVERGENT FLOW W OF THE TROUGH AXIS HAS RESULTED IN INTENSE
DRYING OVER THE NW PART OF THE AREA....WITH THE STRONGEST
SUBSIDENCE COINCIDENT WITH RIDGING FROM THE SOUTHERN GULF
BEGINNING TO SPILL OVER INTO THE NW PART OF THE AREA.  AT THE
SURFACE...LOWER HEIGHTS ALOFT HAVE TRANSLATED LOWER-THAN-NORMAL
PRESSURES ACROSS THE BASIN...RESULTING FROM A DISPLACED AND
FAIRLY LOW-LEVEL RIDGE NE OF THE LESSER ANTILLES.
THE WEAKER-THAN-NORMAL SURFACE RIDGE HAS LED TO REDUCED TRADES
THE LAST FEW DAYS...WITH TRADES TODAY EVEN WEAKER THAN
YESTERDAY.  HOWEVER...EARLIER MICROWAVE PASSES REVEALED E TO SE
20 KT WINDS IN THE GULF OF HONDURAS...LIKELY ENHANCED BY LOW
PRESSURE COMING OUT OF THE PLAINS.

OVER THE NEXT FEW DAYS...MODELS INDICATE THAT THE SHORTWAVE
TROUGH CROSSING THE CENTRAL CARIBBEAN THIS EVENING SHOULD EXIT
THE REGION LATER THIS WEEKEND...REPLACED BY MID- TO UPPER-LEVEL
RIDGING JUST N OF THE AREA.  THIS PATTERN SHOULD FAVOR A
REINVIGORATED SURFACE RIDGE OVER THE SW ATLC...WHICH SHOULD HELP
TRADES INCREASE SLIGHTLY...PERHAPS AT OR JUST BELOW
CLIMATOLOGICAL AVERAGES.  HOWEVER...THE PATTERN LOOKS TO BE A
DRY ONE...WITH NO SPECIFIC AREAS OF ORGANIZED CONVECTION LIKELY
EXCEPT FOR THE DIURNALLY-DRIVEN VARIETY OVER SOME OF THE MAJOR
LANDMASSES NEAR PEAK HEATING.

ATLANTIC OCEAN W OF 40W...
THE WEAK POSITIVELY-TILTED SHORTWAVE TROUGH FROM THE CENTRAL
CARIBBEAN EXTENDS NE INTO THE CENTRAL ATLANTIC TO NEAR 30N52...
PER WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS.  THIS FEATURE
IS CARRYING A WEAK YET COMPLEX FRONTAL SYSTEM N OF 25N BETWEEN
ABOUT 45W AND 65W. MORE SPECIFICALLY...THE MAIN FRONTAL WAVE...
1010 MB...IS LOCATED NEAR 30N46W... WITH AN ILL-DEFINED BOUNDARY
EXTENDING WESTWARD TO A SECOND AND POORLY ORGANIZED SURFACE LOW
NEAR 29N57W.  THE FRONT CONTINUES SW FROM THE LOW TO NEAR 24N71W
...WHERE IT BECOMES STATIONARY. SATELLITE IMAGERY INDICATES
SCATTERED TO WIDESPREAD LOW- TO MID-LEVEL CLOUDS ALONG AND
DIRECTLY AHEAD OF THE FRONT...WITH ISOLATED SHOWERS AND PERHAPS
A TSTM OR TWO POPPING UP WITHIN 90 NM SE OF FRONT BETWEEN 54W
AND 65W. A TIGHT COMMA-SHAPED LEAF IS FORMING IN ASSOCIATION
WITH THE MAIN SURFACE LOW...WITH A SOLID COVERAGE OF OVERRUNNING
RAINS N OF 30N BETWEEN 40W AND 45W. A WEAK PRESSURE GRADIENT
SUPPORTS NO MORE THAN 10- TO 15-KT OF WINDS ACROSS THE
AREA...EXCEPT FOR AROUND 20 KT JUST N OF THE SURFACE WAVE NEAR
THE WESTERNMOST SURFACE...WITH NEAR 25 KT WIND IMMEDIATELY NE OF
THE STRONGER WAVE. MODELS SHOW W ATLANTIC SHORTWAVE COMBINING
WITH A MORE PORTENT NORTHERN STREAM FEATURE THIS WEEKEND...WITH
THE CONSOLIDATED SYSTEM RACING E OF THE AREA BY SUN.  SURFACE
HIGH PRESSURE SHOULD BUILD IN ITS WAKE AND GRADUALLY MIGRATE
FROM W TO E...AS A STRONG COLD FRONT MAKES ITS WAY OFF THE SE
U.S. COAST SUN.

ATLANTIC OCEAN E OF 40W...
BROAD...DEEP-LAYERED CYCLONIC FLOW CONTINUES OVER THE NE
ATLANTIC...GENERALLY N OF 20N E OF 60W. THIS PATTERN SHOULD
CONTINUE INTO THE WEEKEND...AS ONE SYSTEM CURRENTLY MOVING
INLAND OVER NW AFRICA AND THE MEDITERRANEAN IS REPLACED BY THE
SYSTEM CURRENTLY OVER THE CENTRAL ATLANTIC. WITH NO SUBTROPICAL
RIDGE...TRADES HAVE COLLAPSED ACROSS MUCH OF THIS AREA AND ARE
WEAKER-THAN-NORMAL STILL S OF 20 AND E OF 60W.  NO IMPORTANT
CHANGES ARE EXPECTED OVER THE NEXT FEW DAYS...GIVEN THAT THE
PATTERN IS LIKELY TO REINFORCED.

OTHERWISE...AN ELONGATED MID- TO UPPER-LEVEL RIDGE EXTENDS FROM
W AFRICA TO JUST E OF THE LESSER ANTILLES...WITH AN AXIS RUNNING
FROM 20N06W TO 12N53W.  ALTHOUGH CONVECTION HAS DECREASED OVER
THE TROPICAL ATLANTIC THE LAST FEW DAYS...THERE ARE TWO AREAS OF
INTEREST WHICH HAVE EMERGED OVER THE LAST 24 HOURS.  THE FIRST
IS A CONVECTIVE CLUSTER N OF THE ITCZ...WITH WHAT APPEARS TO BE
A MID-LEVEL CYCLONIC CIRCULATION CENTERED NEAR 5N18W MOVING W AT
15 TO 20 KT.  THIS FEATURE COULD BE CONSIDERED ONE OF THE
SEASONS FIRST AFRICAN EASTERLY WAVES.  THE SECOND FEATURE IS
ALONG ELONGATED SURFACE TROUGH OF NORTHEASTERLIES CONVERGING
WITH EASTERLIES BETWEEN 8N AND 10N BETWEEN 45W AND 50W. EARLIER
VISIBLE SATELLITE IMAGERY REVEALED A TIGHTLY-COILED LOW- TO
PERHAPS MID-LEVEL CIRCULATION IN THE ASSOCIATED CONVECTION NEAR
9N46W....THOUGH THE CONVECTION SINCE THAT TIME HAS COLLAPSED.


$$
KIMBERLAIN




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