[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 060556
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 AM EDT SUN APR 06 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
0545 UTC.

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 6N11W 3N20W 1N30W...CROSSING
THE EQUATOR NEAR 34W...TO THE NORTHEASTERN COAST OF BRAZIL NEAR
3S40W.  SCATTERED MODERATE TO SCATTERED STRONG CONVECTION WITHIN
300 NM N OF AXIS BETWEEN 17W AND 24W.  SCATTERED MODERATE
CONVECTION S OF 7N W OF LINE FROM 6N31W TO ITCZ AND W TO 40W.

...DISCUSSION...

THE GULF OF MEXICO...
A SOUTHERN STREAM SHORTWAVE TROUGH PASSING THROUGH THE
SOUTHEASTERN STATES IS DRAGGING A WEAK COLD FRONT ACROSS THE
NORTH CENTRAL AND NE GULF OF MEXICO EARLY THIS MORNING ALONG
30N86W TO 27N89W...WITH A WEAK SURFACE 1011 MB LOW ANALYZED
CLOSE TO 29N87W. THE FRONT CONTINUES SW INTO THE W CENTRAL GULF
OF MEXICO FROM 27N89W TO 23N97W AND THEN BARELY INLAND OVER FAR
NE MEXICO. A 0032 UTC QUIKSCAT PASS DISTINCTLY SHOWS THE FRONT
OVER THE CENTRAL GULF...BUT THE FRONT BECOMES MUCH HARDER TO
IDENTIFY OVER THE W CENTRAL GULF...ONLY GIVEN BY A BROAD
CYCLONIC SHEAR AND A SUBTLE INCREASE TO THE LOW-LEVEL WINDS.
QUIKSCAT DATA OVER THE EASTERN GULF WAS ENTIRELY RAIN-
CONTAMINATED AND THUS NOT RELIABLE FOR PLACING THE FRONT...AS
BOTH SATELLITE AND RADAR IMAGERY SHOW A WELL-ORGANIZED
CONVECTIVE LINE PROPAGATING WELL AHEAD OF THE FRONT ACROSS THIS
AREA AS WELL AS THE CENTRAL FL PENINSULA. HOWEVER...A SINGLE
...NON-FLAGGED OBSERVATION NEAR 25N85W DID SUGGEST A SE INFLOW
OF 35 KT INTO THE CONVECTIVE LINE AT THAT TIME.  ELSEWHERE SE OF
THE FRONT...A GENERAL SE TO S WIND FLOW OF 10- TO 15 KT IS THE
RULE EXCEPT IN THE BAY OF CAMPECHE WHERE NE WINDS 5 TO 10 KT
PREVAIL.  SKIES REMAIN GENERALLY CLOUD-FREE TOO...EXCEPT FOR
OVER PORTIONS OF THE EXTREME SE GULF OF MEXICO WHERE HIGH CLOUDS
ASSOCIATED WITH A LARGE AREA OF CONVECTION OCCURRING OVER THE
EASTERN YUCATAN PENINSULA.  W OF THE FRONT...SURFACE RIDGING IS
NOTED FROM THE UPPER TX COAST INTO NE MEXICO...WITH WHATEVER
STRATUS CLOUDS FROM EARLIER ALMOST ENTIRELY DISSIPATING.

SHORT-MODEL GUIDANCE INDICATES THAT THE SE U.S. SHORTWAVE SHOULD
BEGIN LIFTING OUT TODAY...UNABLE TO DIG FURTHER THANKS TO A
SOLID AREA OF MID-LEVEL RIDGING PARKED OVER THE WESTERN
ATLANTIC. WITH THE MAIN UPPER-LEVEL DYNAMICS SHIFTING NORTHWARD
...EXPECT THE BULK OF THE PRECIPITATION TO FALL FROM GEORGIA
THROUGH THE CAROLINAS WITH THE COVERAGE AND INTENSITY DECREASING
OVER THE EASTERN GULF AND FLORIDA.  HOWEVER...MOIST...LOW-LEVEL
AIR INTERSECTING THE MAIN CONVECTIVE OUTFLOW BOUNDARY MARCHING
DOWN THE SOUTHERN HALF OF FL AND ADJACENT WATERS COMBINED WITH
FAVORABLE UPPER-LEVEL DIVERGENCE SHOULD BE ENOUGH TO SUPPORT
SCATTERED TO LOCALLY NUMEROUS RAIN SHOWERS AND TSTMS ESPECIALLY
AROUND THE TIME OF PEAK HEATING. WITH THE MAIN UPPER SUPPORT
ALREADY WELL NE OF THE AREA AND THE MID- TO UPPER-LEVEL FLOW
BECOMING NEARLY PARALLEL TO THE FRONT...THE FRONT SHOULD STALL
ALONG THE NORTHERN GULF AND N FLORIDA...WITH THE WESTERN END
LOSING ITS IDENTITY. THEREAFTER...MODELS INDICATE THAT A
SEPARATE AND MUCH WEAKER SOUTHERN STREAM SHORTWAVE RACING
THROUGH THE NE GULF SUN EVENING SHOULD SPARK THE DEVELOPMENT OF
A NEW WAVE ALONG THE FRONT OVER THE NE GULF...WHICH SHOULD TRACK
ACROSS N FLORIDA AND EMERGE INTO THE ATLANTIC WATERS AND
EVENTUALLY DRAG THROUGH THE FRONT DOWN THE STATE OF FL MON.

CARIBBEAN SEA...
WATER VAPOR REVEALS HIGH-LEVEL WESTERLY FLOW DOMINATING MUCH OF
THE BASIN...WITH THE REMAINS OF A WEAKENING UPPER-LEVEL TROUGH
LYING FROM 19N80W TO 9N85W. MODERATE TO STRONG UPPER
TROPOSPHERIC SUBSIDENCE ASSOCIATED WITH A LARGE AND DOMINANT
MID- TO UPPER-LEVEL ANTICYCLONE IN THE TROPICAL E PACIFIC
CONTINUES TO BE OBSERVED AS FAR E AS THE WESTERN CARIBBEAN W OF
THE DISSIPATING TROUGH AXIS.  LIKE YESTERDAY...A PLUME OF
MOISTURE WITH ORIGINS FROM CONVECTIVE DEBRIS OVER THE AMAZON IS
BEING DRAWN NORTHWARD FROM NORTHERN COLOMBIA TO JUST SOUTH OF
HISPANIOLA AND PUERTO RICO.  DESPITE THE SUBTLE INCREASE IN
UPPER TROPOSPHERIC MOISTURE AND DIFFLUENT UPPER-LEVEL FLOW...
LITTLE IN THE WAY ON CONVECTION IS NOTED EXCEPT OVER NORTHERN
COLOMBIA EARLIER THIS EVENING. IN FACT...THE ONLY CONVECTION TO
REPORT IS OVER CUBA...WHERE LOCAL SEA BREEZE CIRCULATIONS AND A
GRADUALLY DESTABILIZING ATMOSPHERE LED TO LATE AFTERNOON TSTMS
WHICH ARE DIMINISHING AND BLOWING OFF TO THE NE WITH THE
UPPER-LEVEL WINDS.

OTHERWISE...SURFACE HIGH PRESSURE OVER THE CENTRAL ATLANTIC NEAR
NEAR 29N59W HAS AN EXTENSION INTO THE CARIBBEAN SEA AND IS
PROVIDING A CONTINUED FRESH TRADE WIND FLOW ACROSS THE EASTERN
AND CENTRAL PART OF THE BASIN.  HOWEVER...COMPARED TO LAST
NIGHT...TRADES ARE SLIGHTLY WEAKER THAN 24 HOURS AND ARE CLOSE
TO CLIMATOLOGICAL AVERAGES AS SUGGESTED BY SOME OF THE REAL-TIME
NCEP RE-ANALYSIS DATA.

OVER THE NEXT FEW DAYS...A WELL-DEFINED MID- TO UPPER-LEVEL
RIDGE SHOULD CONTINUE TO PREVAIL N OF THE CARIBBEAN IN THE
VICINITY OF 25N60W.  THIS SHOULD ALLOW FOR A PATTERN OF WEAKER-
THAN-NORMAL WESTERLY FLOW AT UPPER LEVELS ACROSS THE REGION...
WITH NOTABLE EASTERLY WIND ANOMALIES LIKELY THROUGH THE WEEKEND
INTO EARLY NEXT WEEK.  MEANWHILE...THE SURFACE RIDGE OVER THE
CENTRAL ATLANTIC SHOULD GRADUALLY WEAKEN WHILE SHIFTING SSE...
WHICH SHOULD CAUSE THE FRESH TRADE WIND FLOW ACROSS THE AREA TO
RELAX.

ATLANTIC OCEAN....
AN ANOMALOUSLY STRONG MID-LEVEL RIDGE REMAINS LOCKED IN PLACE
OVER THE WEST CENTRAL ATLANTIC NEAR 25N60W...DIRECTING THE
STRONG MID-LATITUDE FLOW OVER THE EASTERN CONUS N OF THE AREA.
INSTEAD THE STRONGER MID-LATITUDE FLOW DIGS EASTWARD INTO A
BROAD...DEEP-LAYERED TROUGH W OF 50 AND N OF ABOUT 15N...WITH AN
ASSOCIATED CLOSED CYCLONIC CIRCULATION NEAR 37N30W. AT THE
LEADING EDGE OF THE TROUGH LIES A SURFACE COLD FRONT EXTENDING
FROM 31N23W TO 23N38W FOLLOWED BY A LARGE DOME OF SURFACE HIGH
PRESSURE CENTERED NEAR 29N59W.  THE STRONG PRESSURE GRADIENT
BETWEEN THE HIGH AND THE LOWER LATITUDES IS RESULTING IN NORMAL
TO ENHANCED TRADES...MOSTLY OVER THE AREA S OF 20N AND W OF 45W
TO THE LESSER ANTILLES. IN FACT...AN EARLY EVENING QUIKSCAT PASS
REVEALED STILL 20- TO 25-KT NE WINDS OVER MUCH OF THE ABOVE
AREA...WITH SEAS GENERALLY 9 TO 12 FT IN NE SWELL. WITH THE
SURFACE RIDGE FORECAST TO GRADUALLY WEAKEN AND SHIFT SSE...THE
FRESH TRADES SHOULD RELAX GOING INTO EARLY NEXT WEEK...WITH SEAS
SUBSIDING TO 6 TO 8 FT BY TUE NEXT WEEK.

W OF 50W...A BROAD SURFACE CYCLONIC FLOW COVERS THE AREA N OF
ABOUT 25N...DIRECTLY BEHIND A COLD FRONT MOVING E OF THE AREA.
OTHER THAN A FAIRLY THICK DECK OF STRATOCUMULUS W OF THE FRONT
...THERE IS LITTLE ELSE THAT DEFINES THIS FEATURE.  AS THE FRONT
RACES FARTHER SE TODAY...A NEW INJECTION OF COOLER AIR SHOULD
BRIEFLY RE-INVIGORATE THE LARGE CYCLONIC CENTER S OF THE AZORES.
THIS...IN TURN...SHOULD KEEP THE CURRENT DEEP-LAYERED CYCLONIC
FLOW OVER THE AREA IN PLACE INTO EARLY NEXT WEEK.

ELSEWHERE...WATER VAPOR IMAGERY AND CLOUD-TRACKED WINDS INDICATE
A NARROW MID- TO UPPER-LEVEL RIDGE S OF ABOUT 12N FROM THE NW
COAST OF AFRICA TO JUST SE OF THE WINDWARD ISLANDS.  THE DEEP
EASTERLIES S OF THE RIDGE ALONG WITH THE PRESENCE OF AN
EQUATORIAL
KELVIN WAVE APPROACHING 0W 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 GRADUALLY DIMINISH BY EARLY NEXT WEEK...ONCE
THE KELVIN WAVE PROPAGATES E OF THE AREA.

$$
KIMBERLAIN




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