[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 231153
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST THU 23 DEC 2004

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN
SECTIONS OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE
AFRICAN COAST FROM THE EQUATOR TO 32N. THE FOLLOWING
INFORMATION IS BASED ON SATELLITE IMAGERY...WEATHER
OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS.

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1115 UTC.

...ITCZ...

ITCZ AXIS ALONG 7N12W 4N25W 4N40W 3N55W.  SCATTERED MODERATE
FROM 3.5N-7N BETWEEN 24.5W-29.5W.  ISOLATED MODERATE WITHIN 45
NM OF 6.5N BETWEEN 12W-20W AND WITHIN 60 NM OF 1N25W.

...DISCUSSION...

GULF OF MEXICO...
LAST PUSH OF ARCTIC AIR FOR A WHILE HAS MOVED INTO THE E GULF
BEHIND A COLD FRONT FROM ABOUT PENSACOLA FLORIDA THRU 25N90W
SURGING THRU E MEXICO NEAR 20N97W.  THICK LOW CLOUDS FOLLOW THE
FRONT ALL THE WAY TO THE COAST AND EARLIER SNOW SHOWERS IN
CENTRAL LOUISIANA HAVE DISSIPATED.  SCATTERED MODERATE
CONVECTION IS N OF 26N E OF THE FRONT ALMOST TO THE W COAST OF
FLORIDA WITH SOME INCREASE OVER THE PAST FEW HOURS AS THE FRONT
ENTERS DEEPER MOISTURE/GREATER INSTABILITY PARTIALLY DUE TO THE
WARM LOOP CURRENT.  ISOLATED SHOWERS/POSSIBLE TSTMS ARE WITHIN
60 NM OF THE FRONT S OF 26N.  TSTMS ARE LIKELY THROUGH THE DAY
IN FLORIDA WITH VERY COLD AIR POURING INTO THE PANHANDLE.  THESE
TSTMS ARE BEING FORCED BY A STRONG MID/UPPER SHORTWAVE MOVING
THRU THE MIDWEST ALONG THE OHIO RIVER NEAR INDIANA TROUGHING S
INTO THE NE GULF.  THE FRONT IS EXPECTED TO PUSH THRU CENTRAL
FLORIDA LATER TODAY AND STALL IN S FLORIDA AS A WAVE OF LOW
PRESSURE DEVELOPS ON THE FRONT IN THE W-CENTRAL GULF OVERNIGHT
FRI.  A LINGERING QUESTION IS WILL THE LOW DEVELOP CLOSE ENOUGH
TO THE COAST TO BRING ANY WINTRY PRECIP TO THE GULF COAST
STATES?  RIGHT NOW THE MODEL TREND HAS BEEN TO KEEP THE LOW A
LITTLE FARTHER SOUTH WHICH WOULD KEEP THE HEAVIEST PRECIP
OFFSHORE OF THE NORTHERN GULF COAST.  THIS SHIFTS THE HIGHEST
THREAT FOR WINTRY WEATHER TO S TEXAS OVERNIGHT FRI IN A
WRAP-AROUND BAND ON THE NW SIDE OF THE DEVELOPING LOW THOUGH
TEMPERATURE PROFILES ARE MARGINAL.  AREAS ALONG THE IMMEDIATE
GULF COAST FROM THE FLORIDA PANHANDLE TO LOUISIANA SHOULD KEEP A
WATCH ON THE SITUATION AS IT WOULD ONLY TAKE A SMALL SHIFT IN
THE LOW TRACK TO BRING A BETTER CHANCE OF MIXED PRECIP TO AREAS
THAT RARELY RECEIVE IT...ESPECIALLY ON XMAS EVE!  PEOPLE WHO
LIKE THE COLD WEATHER SHOULD ENJOY IT WHILE IT LASTS AS A
PATTERN SHIFT IS ON THE WAY IN THE MEDIUM RANGE AS A NEGATIVE
PNA PATTERN DEVELOPS OVER THE CONUS...BRINGING MUCH WARMER
WEATHER BY EARLY NEXT WEEK.

WEST ATLANTIC...
DISSIPATING STATIONARY FRONT EXTENDS FROM 31N56W TO 23N67W NE OF
THE BAHAMAS.  WIDELY SCATTERED WEAK CONVECTION IS N OF 23N
BETWEEN 55W-61W.  GENERALLY SCATTERED LOW CLOUDS ARE N OF 22N W
OF THE FRONT WITH DECREASING CLOUDINESS OVER THE BAHAMAS.  ZONAL
UPPER FLOW IS OVER THE AREA WITH A WEAK UPPER DISTURBANCE NEAR
32N62W PROVIDING A BIT OF UPPER LIFT FOR SHOWERS/ISOLATED TSTMS
NEAR THE DYING FRONT.  OTHERWISE...SURFACE ELY FLOW TO 25 KT
PERSISTS AS HIGH PRESSURE ALONG 40N THRU THE ATLC WATERS KEEPS
THE PRESSURE GRADIENT TIGHTER-THAN-AVERAGE IN THE AREA.

CARIBBEAN SEA...
VERY DRY AIR IN THE MID/UPPER LEVELS DOMINATES WITH ZONAL FLOW
CONTINUING.  STATIONARY MID/UPPER HIGH IS OVER NW VENEZUELA WITH
SOMEWHAT ANTICYCLONIC FLOW COVERING THE AREA S OF 15N.
TRADEWINDS SHOWERS ARE CONCENTRATED ALONG 70W WITHIN 75 NM OF A
WEAK LOW-LEVEL CONVERGENCE ZONE AS WELL AS SOME SHOWERS S OF 15N
W OF 82W AND IN THE LESSER ANTILLES E OF 65W.  THESE SUBTLE
FEATURES ARE THE RULE WITH NO SYNOPTIC-SCALE SYSTEMS FORECAST TO
AFFECT THE AREA THRU THE WEEK.

CENTRAL/E ATLANTIC...
1010 LOW HAS FORMED AROUND 24N32W ALONG NW-SE ORIENTED SURFACE
TROUGHING EXTENDING THE LOW NW TO 32N40W.  BAND OF WIDELY
SCATTERED WEAK/MODERATE CONVECTION IS ALONG AND E OF THE TROUGH
WITHIN 240 NM.  THE UKMET/GFS HINT AT THE POSSIBILITY OF
SUBTROPICAL CHARACTERISTICS SLOWLY DEVELOPING NEAR THE
LOW...PERHAPS BEST NEAR XMAS.  THE SYSTEM WILL BE WATCHED THOUGH
COOL WATERS TEMPS ARE RATHER MARGINAL FOR EVEN A HYBRID
DEVELOPMENT.  IN THE CENTRAL ATLC TROUGH...MOST OF THE UPPER
ENERGY HAS PULLED OUT OF THE DEEP TROPICS...SHIFTING THE BULK OF
THE PRECIP TO THE SUBTROPICAL ATLC THOUGH WIDELY SCATTERED
MODERATE REMAINS FROM 10N-15N BETWEEN 29W-36W.  DEEP MID/UPPER
LOW NEAR 29N40W SUPPORTS THE LARGE-SCALE DISTURBED WEATHER WITH
A SHORTWAVE JUST TO THE W OF THE SURFACE LOW PROVIDING THE
IMPETUS FOR THE SURFACE DEVELOPMENT.  DRY WLY FLOW IS W OF 40W
WITH SOME THICKENING HIGH CLOUDS W OF 50W N OF 20N FROM DISTANT
RAIN ACTIVITY NEAR A RIDGE AXIS ALONG 54W.  THIS DRY AIR IS
KILLING ANY SIGNIFICANT PRECIP IN THE ITCZ W OF 40W ALONG WITH
UPPER CONVERGENCE.  IN THE E ATLC... LARGE AREA OF HIGH CLOUDS
IS E OF 30W/FEW SHOWERS S OF 20N WITH MID/UPPER RIDGING ALONG
THE W AFRICAN COAST EXCEPT FOR A MID/UPPER LOW NEAR 30N11W
SUPPORTING ISOLATED SHOWERS NEAR AND NE OF THE CANARY ISLANDS.

$$
BLAKE

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