[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 111747
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT TUE MAR 11 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1745 UTC.

...THE ITCZ...

ITCZ AXIS IS CENTERED ALONG 7N13W 4N20W CROSSING THE EQUATOR
NEAR 26W THEN ALONG 2S30W TO 3S41W. CLUSTERS OF SCATTERED
MODERATE/STRONG CONVECTION ARE FROM 1W-14W BETWEEN THE THE COAST
OF SW AFRICA TO ACROSS THE EQUATOR. SCATTERED MODERATE
CONVECTION IS WITHIN 75 NM OF 5N W FROM 47-51W TO INLAND OVER
SOUTH AMERICA.

...DISCUSSION...

GULF OF MEXICO...
A WEAK SHORTWAVE TROUGH OVER THE LOWER MISSISSIPPI VALLEY THIS
MORNING SHOULD TREK EAST-NORTHEAST AND BECOME ABSORBED BY A MORE
DOMINANT NORTHERN STREAM SHORTWAVE EARLY WEDNESDAY.  AS IT DOES
SO...IT SHOULD HELP DRAG A WEAK ASSOCIATED COLD FRONT LOCATED
ALONG 29N89W 28N90W 24N93W 20N97W THROUGH THE REMAINDER OF THE
WESTERN AND CENTRAL GULF LATER TODAY AND THIS EVENING AND CARRY
AN ASSOCIATED 1018MB SURFACE LOW FROM 29N90W INTO THE NE GULF.
HOWEVER...THE COLD SHOULD ONLY MAKE SLOW SEWD PROGRESS TONIGHT
AND EARLY...UNTIL A SECOND SOUTHERN STREAM SHORTWAVE MOVING
THROUGH THE SOUTHERN PLAINS REACHES THE GULF COAST EARLY WED AND
DRIVES THE FRONT THROUGH THE REMAINDER OF THE GULF AND FLORIDA
TO A POSITION 31N70W 22N81W 21N88W EARLY WED AFTERNOON. A
PATTERN OF WEAK...LARGE-SCALE DIVERGENCE ALOFT...RIGHT REAR
QUADRANT DYNAMICS...AND OVERRUNNING MOISTURE AHEAD OF THIS
SYSTEM IS DRIVING SCATTERED LIGHT TO MODERATE CONVECTION FROM
NEAR THE MOUTH OF THE MS RIVER THIS MORNING TO THE FLORIDA
PANHANDLE. ADDITIONAL SHOWERS AND TSTMS ARE DEVELOPING IN THE
BAY OF CAMPECHE AND SW GULF...WHERE THE ELY TRADES ARE MEETING
THE NLY FLOW BOTH AHEAD AND BEHIND THE FRONT. FARTHER EAST...
SHOWERS AND TSTMS HAVE ALSO BROKEN OUT FROM NEAR THE DRY
TORTUGAS THROUGH THE LOWER FLORIDA KEYS AND FLORIDA BAY...AHEAD
OF WHAT ONCE WAS LIKELY THE OLD POLAR FRONT. HOWEVER...LOW-LEVEL
WINDS SHOW LITTLE...IF ANY CYCLONIC SHEAR AT THIS TIME...WHICH
MAY SUGGEST THAT THIS CONVECTION IS DEVELOPING NEAR AND AHEAD OF
THE 850MB FRONT BEING TO RETURN NEWD.

AS THE SECOND SRN STREAM SHORTWAVE RIDES THROUGH N FL LATE
WED...THE COLD FRONT SHOULD CONTINUE EWD THROUGH SW ATLC BUT
BECOME STATIONARY THROUGH THE SRN GULF.  NEW HEIGHT FALLS AHEAD
OF YET ANOTHER SHORTWAVE PUSHING THROUGH THE ROCKIES SHOULD
CAUSE THE WRN PORTION OF THE BNDRY TO RETURN AS A WARM BY
THU...WITH MODEL GUIDANCE SUGGESTING A FAIR AMOUNT OF CONVECTION
FORMING AHEAD OF THE RETREATING BOUNDARY OVER THE WEST CENTRAL
GULF.

CARIBBEAN SEA...
A FLAT MID- TO UPPER-LEVEL RIDGE OF HIGH PRESSURE COVERS THE
BASIN...WITH AN AXIS ALONG 15N-16N. DEEP 200MB EASTERLIES...AND
ANOMALOUS EASTERLIES AT THAT... EXIST SOUTH OF THE RIDGE AXIS
COVER MUCH OF NRN SOUTH AMERICA AND THE SOUTHERN CARIBBEAN. THIS
PATTERN OF ELY UPPER-LEVEL FLOW DEVELOPING SO EARLY COULD BE
PARTIALLY RELATED TO THE STRONG COLD EVENT OCCURRING IN THE
PACIFIC.  ELSEWHERE...STRONG ZONAL FLOW ALOFT FROM FLORIDA
THROUGH THE WESTERN ATLANTIC HAS RESULTED IN LOWER SURFACE
PRESSURES OVER THE AREA COMPARED TO LAST WEEK AND THIS WEEKEND.
THE RESULT HAS BEEN A BREAK IN THE MODERATE TO STRONG SURFACE
RIDGE WHICH HAS BEEN IN PLACE FOR MUCH OF THE FIRST WEEK OF
MARCH. IN TURN...THIS HAS LED TO A GENERAL REDUCTION OF THE
TRADE WIND FLOW BASIN WIDE EARLY THIS WEEK...WITH 15- TO 20-KT
WINDS IN PLACE OF 20- TO 25-KT WINDS.  EVEN WINDS OFF THE COAST
OF COLOMBIA HAVE DECREASED MARKEDLY...WITH 20- TO OCCASIONALLY
25-KT WINDS INSTEAD OF 30-KT WINDS.

OTHERWISE...THE GULF FRONT DESCRIBED ABOVE SHOULD REACH THE NE
YUCATAN/YUCATAN CHANNEL EARLY WED AND COME TO A HALT AS 500MB
HEIGHTS BEGIN RISING OVER THE GULF AHEAD OF A NEW JET STREAM
IMPULSE MOVING OUT OF THE WEST.


ATLANTIC OCEAN...
A NRN STREAM SHORTWAVE...EXTENDING FROM EAST OF THE CANADIAN
MARITIMES SOUTHWESTWARD INTO THE WRN ATLC...IS DRIVING AN
ASSOCIATED COLD FRONT ALONG 31N54W 28N60W SLOWLY EWD.
MEANWHILE...THE SRN END OF THE BOUNDARY REMAINS STATIONARY FROM
28N60W TO 24N77W BUT SHOULD BEGIN LIFTING NORTH AND EAST AS A
WARM FRONT LATER TODAY AND WED IN RESPONSE TO A SHORTWAVE MOVING
OUT OF THE SRN PLAINS TO THE NE GULF COAST DURING THE NEXT 24
HOURS. WARM AIR ADVECTION...OVERRUNNING MOISTURE...AND POSITIVE
VORTICITY ADVECTION AHEAD OF THIS JET STREAM DISTURBANCE SHOULD
LEAD TO SCATTERED CONVECTIVE ACTIVITY NORTH OF THE RETREATING
BOUNDARY...FIRST OVER THE SOUTHERN HALF OF FLORIDA AND THE NWRN
BAHAMAS AND THEN ULTIMATELY FARTHER NE. CONVECTIVE STORMS SHOULD
ALSO FIRE UP AHEAD OF THE COLD FRONT MOVING OFF THE FL COAST
EARLY WED AND AFTERNOON AND REMAIN SCATTERED ALONG THE
BOUNDARY...AS IT BECOMES STATIONARY OVER THE CENTRAL BAHAMAS THU
AFTERNOON.  THE NRN END OF THE BOUNDARY CURRENTLY OVER THE
BAHAMAS SHOULD CONTINUE TRACKING EWD WED AND THU...LYING FROM
31N39W TO 27N51W BY WED AFTERNOON AND FROM 31N30N TO 28N39W THU
AFTERNOON.

ELSEWHERE...MID- TO UPPER-LEVEL HIGH PRESSURE OVER THE CARIBBEAN
TODAY SHOULD BUILD EWD INTO THE TROPICAL ATLC MIDDLE AND LATE
WEEK...REPLACING THE CURRENT SHORTWAVE TROUGH LYING FROM 28N41W
TO 11N60W.  THIS SHOULD PROMOTE AN ANOMALOUS ELY FLOW REGIME AT
UPPER-LEVELS SOUTH OF 10N ACROSS MUCH OF THE TROPICAL ATLC. IN
ADDITION... LOW-LEVEL RIDGING OVER THE SUBTROPICAL ATLC HAS
WEAKENED SUBSTANTIALLY SINCE LAST WEEK AND THIS WEEKEND...WITH
WHAT REMAINS OF THE RIDGE STRONGEST OVER THE EXTREME ERN PART OF
THE BASIN. THIS HAS RESULTED IN A GENERAL RELAXATION OF ELY
TRADES S OF 20N...WITH TRADES AT OR BELOW CLIMATOLOGICAL LEVELS.

$$
KIMBERLAIN




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