[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 121800
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT WED MAR 12 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 7N12W 2N20W CROSSING THE
EQUATOR NEAR 26W TO 5S36W. CLUSTERS OF SCATTERED MODERATE/
STRONG CONVECTION ARE OCCURRING FROM THE COAST OF SW AFRICA TO S
TO THE EQUATOR BETWEEN 2E AND 23W. ADDITIONAL SCATTERED
LIGHT/MODERATE CONVECTION IS ACTIVE FROM THE EQUATOR TO 2N
BETWEEN 26W AND 30W.

...DISCUSSION...

GULF OF MEXICO...
A VIGOROUS SRN STREAM SHORTWAVE TROUGH NEAR THE CENTRAL GULF
COAST THIS MORNING SHOULD DART EAST INTO THE WRN ATLC AND WEAKEN
BY EARLY THU. AS IT DOES SO...THE IMPULSE SHOULD HELP DRAG A
WEAK COLD FRONT CURRENTLY EXTENDING FROM 31N74W TO 26N83W
THROUGH THE FL PENINSULA TODAY AND THROUGH THE CENTRAL BAHAMAS
BY LATE THU. THE SOUTHERN END OF THE FRONT EXTENDING FROM 26N83W
TO 20N93W AND THEN SOUTHWARD THROUGH THE ISTHMUS OF TEHUANTEPEC
SHOULD REMAIN ESSENTIALLY STATIONARY OR SLOWLY EDGE SE...AS THE
MAIN UPR SUPPORT QUICKLY HEADS EAST OF THE AREA AND THE MID- TO
UPPER-LEVEL WINDS BECOME PARALLEL TO THE FRONT. 1046 UTC AND
1226 UTC QUIKSCAT PASSES OVER THE GULF REVEAL A WEAK WIND REGIME
OVER THE AREA...WITH THE HIGHEST WINDS OF 10 TO 15 KT DIRECTLY
BEHIND THE FRONT AND IN EXTREME ERN GULF AND IN THE SW GULF/BAY
OF CAMPECHE. SATELLITE IMAGERY REVEALS SCATTERED MOSTLY LOW- TO
MID-LEVELS CLOUDS OVER THE BAY OF CAMPECHE...WHERE EASTERLY
TRADES MEET NORTHERLY FLOW BEHIND THE FRONT.  LOW CLOUDS ARE
ALSO BANKED UP AGAINST THE SIERRA MADRE OCCIDENTAL IN MEXICO...
REFLECTING A CONTINUED WEAK UPSLOPE FLOW.

FARTHER UPSTREAM....AN ILL-DEFINED SHORTWAVE TROUGH PASSING
THROUGH THE SW CONUS/NRN MEXICO SHOULD PUSH INTO THE SRN PLAINS
THU...WHILE A STRING OF AMORPHOUS SHORTWAVE ENERGY PROPAGATES
OUT OF THE CENTRAL ROCKIES.  IN RESPONSE TO THESE DEVELOPMENTS
ALOFT...A 1022 MB SURFACE RIDGE CURRENTLY NEAR THE CENTRAL TX
COAST SHOULD MIGRATE RAPIDLY EWD TO NRN FLORIDA BY THU MORNING
AND BE REPLACED WITH A STRENGTHENING RETURN FLOW OVER THE WRN
HALF OF THE GULF AS LOW PRESSURE FORMS IN THE SRN PLAINS.
FALLING HEIGHTS AND A PATTERN OF WARM AIR ADVECTION OVER THE SRN
PLAINS/WRN GULF COAST SHOULD FORCE THE NEARLY STATIONARY
BOUNDARY PRESENTLY OVER THE SOUTHERN GULF TO RETURN AS A WARM
FRONT EITHER LATE TONIGHT OR EARLY THU MORNING.  EXPECT
OVERRUNNING CLOUDS AND THE CHANCE FOR SCATTERED SHOWERS AND
ISOLATED TSTMS NEAR AND NORTH OF THE BOUNDARY...WHICH SHOULD
LIFT TO NEAR THE NRN GULF COAST BY FRI MORNING.

CARIBBEAN SEA...
A FLAT BUT BROAD...MID- TO UPPER-LEVEL ANTICYCLONE LYING JUST OF
THE LESSER ANTILLES DOMINATES MUCH OF THE CARIBBEAN BASIN THIS
MORNING...WITH A RIDGE AXIS BETWEEN 16-17N.  WATER VAPOR IMAGERY
INDICATES THAT STRONG SUBSIDENCE ALOFT ASSOCIATED WITH THIS
FEATURE COVERS THE ENTIRE REGION...WITH THE STRONGEST SUBSIDENCE
CONCENTRATED OVER THE SW CARIBBEAN SEA.  THE SAN JUAN 12 UTC
SOUNDING SHOWS A STRONG TRADE WIND INVERSION AROUND 750MB...WITH
EXTREMELY STABLE AND DRY AIR ABOVE THAT LEVEL. AS A RESULT...
THERE ARE FEW IN THE WAY OF CLOUDS OR SHOWERS ACROSS THE
CARIBBEAN THIS MORNING EXCEPT FOR SOME FROM 15N AND 18N BETWEEN
70W AND 77W.

A STRONG ZONAL FLOW NORTH OF THE CARIBBEAN HAS LED TO A BREAK
DOWN OF THE STRONG LOW-LEVEL SUBTROPICAL RIDGE...WHICH HAD
PERSISTED FROM THE CENTRAL ATLC INTO THE CARIBBEAN SEA FOR MUCH
OF THE FIRST WEEK OF MARCH. CONSEQUENTLY....TRADES ACROSS THE
CARIBBEAN ALSO REMAIN WEAK...ESPECIALLY WHEN COMPARED TO THE
ANOMALOUSLY STRONG TRADE WIND CONDITIONS DURING THE LAST SEVERAL
WEAK.  A 1046 UTC QUIKSCAT PASS SHOWS THE STRONGEST WINDS OF 15
TO 20 KT GENERALLY S OF 16N BETWEEN 70W AND 79W.  AS IS TYPICAL
...STRONGER WINDS OF UP TO 25 KT LIE NEAR BUT OFFSHORE THE COAST
OF COLOMBIA.  THE LIGHTEST WINDS LIE OVER THE NW PART OF THE
BASIN...WHERE LIGHT NE TO E WINDS OF 5 TO 10 KT HAVE DEVELOPED
IMMEDIATELY AHEAD OF THE COLD FRONT DRIFTING SEWD ACROSS THE SRN
GULF.  EXPECT A WEAK TRADE WIND REGIME TO CONTINUE THROUGH AT
LEAST FRI BEFORE SHOWING SIGNS OF RESTRENGTHENING SOME LATER
THIS WEEKEND.

ATLANTIC OCEAN...
THE SHORTWAVE TROUGH ACROSS THE GULF THIS MORNING IS PUSHING A
COLD FRONT INTO THE SW ATLC AND DOWN THE STATE OF FL...WHILE
LIFTING A WARM FRONT AROUND 30N BETWEEN 65W AND 74W NORTH OF
THE AREA. ALTHOUGH FEW...IF ANY...CLOUDS DEFINE THE COLD FRONT
OVER FL...UPPER-LEVEL DIVERGENCE AND RIGHT REAR JET DYNAMICS
NORTH OF THE BAHAMAS ARE FORCING SCATTERED MODERATE TO NUMEROUS
SHOWERS AND TSTMS AHEAD OF IT...WITHIN 90NM EITHER SIDE OF A
LINE RUNNING FROM 31N69W TO 28N75W. IN ADDITION...A 1046 UTC
QUIKSCAT PASS REVEALS 25- TO 30-KT SWLY FLOW WITHIN ABOUT 120NM
SE OF THE FRONT N OF 28N. MODEL GUIDANCE SHOWS THE FRONT
CONTINUING EWD TODAY AND TONIGHT...ENDING UP ALONG AN AXIS FROM
31N61W TO 26N76W TO 23N78W BY THU MORNING...WITH STRONG SWLY
FLOW LIKELY PRECEDING IT THROUGH THU.

ANOTHER FRONT EXTENDS FROM 31N43W TO 28N56W...WHERE IT ATTACHES
ITSELF TO THE WARM FRONT LIFTING NE OVER THE SW ATLC.  THE FRONT
SHOULD CONTINUE EWD TODAY...MOVING EAST OF THE AREA BY THU WITH
LITTLE FANFARE.

OTHERWISE...THE TAIL OF A SHORTWAVE TROUGH EAST OF THE AREA THIS
MORNING EXTENDS THROUGH 15N39W AND FINALLY TO 12N60W. THIS
FEATURE SHOULD EXIT THE AREA ENTIRELY BY THU EVENING...LEAVING
THE
BROAD BUT FLAT MID- TO UPPER-LEVEL RIDGE OVER THE CARIBBEAN TO
EWD 30W BUT SOUTH OF 20N.  THIS PATTERN FAVORS ANOMALOUS
EASTERLY FLOW AT 200MB SOUTH OF ABOUT 16N FROM THE TROPICAL ATLC
THROUGH MUCH OF THE CARIBBEAN SEA AND IS THOUGHT TO BE RELATED
TO THE STRONG AND MATURE LA NINA EVENT IN THE PACIFIC.

$$
KIMBERLAIN




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