[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 061107
TWDAT

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

...THE ITCZ...
THE ITCZ AXIS IS CENTERED ALONG 9N13W 4N20W 1N30W...CROSSING
THE EQUATOR NEAR 26W...TO THE NORTHEASTERN COAST OF BRAZIL NEAR
6S35W.  SCATTERED MODERATE SCATTERED STRONG CONVECTION WITHIN
240 NM N AND 120 NM S OF AXIS BETWEEN 17W AND 24W.  SCATTERED
MODERATE CONVECTION FROM EQUATOR TO 7N BETWEEN 30W AND 40W.

...DISCUSSION...

THE GULF OF MEXICO...
A SOUTHERN STREAM SHORTWAVE TROUGH PASSING THROUGH THE SOUTH-
EASTERN STATES SUPPORTS A WEAK COLD FRONT ACROSS THE NORTH
CENTRAL AND NE GULF OF MEXICO THIS MORNING.  WITH THE MAIN
UPPER-LEVEL SUPPORT NOW NE OF THE AREA...THE FRONT HAS BECOME
NEARLY   STATIONARY FROM 30N86W TO A WEAK SURFACE 1011 MB LOW
ANALYZED CLOSE TO 29N86W AND THEN EXTENDS SW TO 24N97W AND THEN
BARELY INLAND OVER FAR OVER FAR NE MEXICO. EARLIER QUIKSCAT
PASSES AND MORE RECENT ASCAT IMAGERY EASILY DEPICTS THE FRONT
OVER THE CENTRAL GULF...BUT THE FRONT BECOMES MUCH HARDER TO
IDENTIFY OVER THE W CENTRAL GULF...WITH THE ONLY EVIDENCE A
BROAD CYCLONIC SHEAR AND A SUBTLE INCREASE TO THE LOW-LEVEL
WINDS. MICROWAVE DATA OVER THE EASTERN GULF WAS ALMOST ENTIRELY
RAIN-CONTAMINATED AND THUS NOT RELIABLE FOR PLACING THE
FRONT...EXCEPT FOR A FEW DATA POINTS IN A 0326 UTC ASCAT PASS.
THESE DATA INDICATED A SW TO W 20- TO 30-KT INFLOW INTO A
WELL-ORGANIZED CONVECTIVE LINE PROPAGATING WELL AHEAD OF THE
FRONT OVER THE EASTERN GULF AND CENTRAL AND NOW SOUTHERN
FL. LATEST SURFACE OBS...BUOY...AND CMAN OBSERVATIONS REVEAL A
NE-SW ORIENTED OUTFLOW BOUNDARY AT THE LEADING EDGE OF THE
CONVECTIVE LINE...MOVING OFFSHORE THE SE FL COAST AND KEYS AS OF
0900 UTC AND FOLLOWED BY A LARGE AREA OF STRATIFORM
PRECIPITATION. FOWEY ROCKS LIGHT REPORTED A NW 40-KT WIND
IMMEDIATELY AFTER ITS PASSAGE AND A LARGE PRESSURE SPIKE...WITH
SURFACE OBSERVATIONS OVER SOUTHERN FL SUGGESTING A WELL-DEFINED
MESO-HIGH IN THE CONVECTIONS WAKE.

ELSEWHERE SE OF THE FRONT...NEW CONVECTION IS DEVELOPING WITHIN
90 NM SE OF THE BOUNDARY BETWEEN 26N AND THE WEAK SURFACE WAVE.
IN FACT...WITHIN THE LAST HOUR...LIGHTNING DATA REVEALS A NEW
EXPLOSION OF LIGHTNING STRIKES WITHIN THIS AREA...LIKELY
SIGNALING THE FORMATION OF A NEW CONVECTIVE COMPLEX FOR LATER
TODAY.  OTHERWISE...A SE TO S WIND FLOW OF 10- TO 15 KT
GENERALLY PREVAILS EXCEPT IN THE BAY OF CAMPECHE THE FLOW SHIFTS
MORE NE AND THUS MORE CYCLONIC AROUND A MECHANICALLY-FORCED LOW.
SKIES REMAIN GENERALLY CLOUD-FREE TOO...EXCEPT FOR SCATTERED LOW
CLOUDS OVER THE S CENTRAL AND SW GULF.  W OF THE FRONT...SURFACE
RIDGING IS NOTED FROM THE UPPER TX AND SW LOUISIANA COASTS INTO
NE MEXICO...WITH SCATTERED STRATUS CLOUDS ACROSS THE AREA.

SHORT-MODEL GUIDANCE INDICATES THAT THE SE U.S. SHORTWAVE SHOULD
LIFT 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 GENERALLY DECREASING OVER THE
EASTERN GULF AND FLORIDA.  HOWEVER...A MOIST LOW-LEVEL FLOW
INTERSECTING THE BOUNDARY ALONG WITH A PATTERN OF FAVORABLE
DIVERGENCE ALOFT SHOULD BE ENOUGH TO SUPPORT SCATTERED TO
LOCALLY NUMEROUS RAIN SHOWERS AND TSTMS ACROSS THE EASTERN GULF
AND FL AROUND THE TIME OF PEAK HEATING. NOW THAT THE MAIN UPPER
SUPPORT IS ALREADY WELL NE OF THE AREA AND THE MID- TO UPPER-
LEVEL FLOW HAS BECOME NEARLY PARALLEL TO THE FRONT...THE FRONT
SHOULD REMAIN NEARLY STATIONARY 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 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
SLIGHTLY DIFFLUENT UPPER-LEVEL FLOW...LITTLE IN THE WAY OF
CONVECTION IS NOTED EXCEPT OVER NORTHERN COLOMBIA YESTERDAY
EVENING. IN FACT...THE ONLY CONVECTION OF CONSEQUENCE WAS OVER
CUBA LATE YESTERDAY...WHERE LOCAL SEA BREEZE CIRCULATIONS AND A
GRADUALLY DESTABILIZING ATMOSPHERE LED TO LATE AFTERNOON TSTMS.

OTHERWISE...A 1026 MB SURFACE HIGH PRESSURE OVER THE CENTRAL
ATLANTIC NEAR NEAR 29N62W 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 EARLY YESTERDAY...TRADES ARE SLIGHTLY WEAKER AND ARE CLOSER
TO CLIMATOLOGICAL AVERAGES AS SUGGESTED BY SOME OF THE REAL-TIME
NCEP RE-ANALYSIS DATA. ELSEWHERE...ASCAT AND HIGH RESOLUTION
QUIKSCAT OVERNIGHT INDICATED STRONG E TO SE 25-KT WINDS OVER THE
GULF OF HONDURAS...AND RECENT SURFACE OBSERVATIONS SHOW A WEAK
SURFACE LOW ALONG THE NORTHERN HONDURAN COAST NEAR 16N87W. THIS
FEATURE AND THE DEVELOPMENT OF THESE STRONG WINDS COULD BE A
CONSEQUENCE OF WHATEVER CONVECTIVE OUTFLOW PUSHED OFF THE
YUCATAN PENINSULA LATE LAST NIGHT AND EARLY THIS MORNING.

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 31N21W TO 21N37W FOLLOWED BY A LARGE DOME OF SURFACE HIGH
PRESSURE CENTERED NEAR 29N62W.  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...EARLIER QUIKSCAT PASSES
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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