[Tropical] Tropical Weather Discussion

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AXNT20 KNHC 241154
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
705 AM EST FRI 24 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 IS ALONG 7N14W 4N25W 4N40W 2N51W.  WIDELY SCATTERED
WEAK/MODERATE S OF 3N BETWEEN 27W-39W.  SIMILAR CONVECTION
WITHIN 75 NM OF LINE 5.5N10W 4.5N25W.

...DISCUSSION...

GULF OF MEXICO...
COLD AIR ADVECTION CONTINUES THIS MORNING IN THE DEEP SOUTH WITH
FREEZING TEMPERATURES TOUCHING THE NORTHERN GULF WATERS.  FRONT
RESPONSIBLE FOR ALL THE CHILLY WEATHER LIES FROM S-CENTRAL
FLORIDA NEAR PUNTA GORDA TO JUST NW OF YUCATAN INTO THE BAY OF
CAMPECHE NEAR 18N94W WITH OVERCAST MULTILAYER CLOUDS COVERING
THE ENTIRE AREA W OF THE FRONT.  PARTLY TO MOSTLY CLOUDY
CONDITIONS ARE AHEAD OF THE FRONT WITH A FEW SHOWERS AND RATHER
MUGGY AIR IN THE SE GULF.  SOUTHERN END OF THE FRONT IS BACKING
UP A TAD AS A SURFACE TROUGH SETS UP IN THE W GULF. SUBTROPICAL
JET IS SENDING TONS OF MOISTURE ACROSS MEXICO OVER THE NW
GULF...SIGNS OF AN OVERRUNNING PATTERN OVER THE COLD AIR DOME
WITH SCATTERED RAIN/SNOW SHOWERS OVER TEXAS WITH ISOLATED RAIN
SHOWERS FORMING WITHIN 150 NM OF THE COAST FROM NW FLORIDA TO SE
TEXAS.  UPPER DISTURBANCE RESPONSIBLE FOR THE CLOUDS/LIGHT RAIN
IS SHIFTING EASTWARD OVER N MEXICO WHICH SHOULD FORM A SURFACE
LOW IN THE W-CENTRAL GULF LATER TODAY.  THERMAL PROFILES ARE
MARGINAL FOR WINTRY PRECIP WITH LIMITED MOISTURE KEEPING THE
BULK OF THE PRECIP OFFSHORE ANYWAY.  BEST CHANCE OF SIGNIFICANT
WINTRY WEATHER MIGHT BE WHEN TEMPERATURES COOL UNDER THE UPPER
SYSTEM IN S TEXAS OVERNIGHT XMAS DAY.  LIGHT MIXED PRECIP COULD
OCCUR THROUGHOUT TODAY INTO XMAS ALONG IMMEDIATE AREAS OF THE
NORTHERN GULF COAST FROM NW FLORIDA THRU INLAND S TEXAS.  RECENT
RADAR IMAGES SHOW BANDS OF POSSIBLE RAIN/SLEET SHOWERS MOVING
INTO NW FLORIDA BETWEEN PANAMA CITY AND DESTIN WITHIN 45 NM OF
LINE 30.5N85W TO THE SE TIP OF LOUISIANA. BIG WEATHER CHANGE IS
LIKELY AFTER THE WEEKEND WITH A NEGATIVE PNA PATTERN (WESTERN
UPPER TROUGH/ EASTERN UPPER RIDGE) DEVELOPING OVER THE CONUS...
BRINGING MUCH WARMER WEATHER BY EARLY NEXT WEEK.

CARIBBEAN SEA AND W ATLC W OF 60W...
VERY DRY AIR IN THE MID/UPPER LEVELS DOMINATES THE CARIBBEAN
WITH WLY FLOW FROM INCREASING RIDGING OVER THE AREA BRIDGING NE
INTO THE W ATLC.  FEW POCKETS OF SHOWERS ARE STREAMING WESTWARD
THRU THE AREA OTHERWISE LESS RAIN THAN AVERAGE.  DEWPOINTS HAVE
DROPPED IN PUERTO RICO AND THE NORTHERN LEEWARD ISLANDS TODAY AS
A BIT OF DRIER AIR FILTERS INTO THE AREA.  NO SYNOPTIC-SCALE
SYSTEMS ARE FORECAST TO AFFECT THE CARIBBEAN THRU THE WEEK OTHER
THAN THE FRONT ENTERING THE NW CARIBBEAN LATE XMAS DAY.  A
DEEPENING TROUGH IN THE CENTRAL ATLC HAS LEFT THE W ATLC ON THE
DRY CONVERGENT SIDE OF THE UPPER TROUGH AXIS WITH DECREASING
MID/UPPER MOISTURE FROM W TO E AND NW FLOW ALOFT.  CONSIDERABLY
LESS CLOUDINESS IS OVER THE W ATLC WITH ONLY SCATTERED LOW
CLOUDS AS ALL OF THE COLD AIR HAS MODIFIED OVER WARM WATERS.
COLD FRONT EXTENDS FROM S-CENTRAL FLORIDA TO 32N78W WITH A FEW
SHOWERS AND OVERCAST CLOUDS BLANKETING THE AREA BEHIND THE
FRONT.  WEAK TROUGH IS AHEAD OF THE FRONT BY ABOUT 60 MILES WITH
WIDELY SCATTERED SHOWERS WITHIN 45 NM OF LINE 27N80W 32N75W.

CENTRAL/E ATLANTIC...
1008 MB LOW IS ALONG A SURFACE TROUGH FROM THE LOW TO 28N51W
WITH GALE-FORCE WINDS N OF THE LOW AND TROUGH.  DEEP MID/UPPER
LOW NEAR 29N39W CONTINUES TO PROVIDE LIFT/DIVERGENCE FOR A BAND
OF WIDELY SCATTERED WEAK/MODERATE CONVECTION WITHIN 90 NM OF
LINE 24N27W 28N31W 31N40W.  COMPUTER MODELS SUGGEST THE LOW WILL
CONTINUE TO TRACK WNW WITH THE LOW PROBABLY STAYING MORE
EXTRATROPICAL THAN SUBTROPICAL.  OF COURSE NOW THE MODELS ARE
HINTING AT THE POSSIBILITY OF ANOTHER LOW FORMING IN A COUPLE
DAYS NEAR 25N45W OUT OF A MESS OF MOISTURE NOW IN THE CENTRAL
ATLC.  I GUESS THIS IS WHAT HAPPENS WHEN THE ATLC OCEAN IS MUCH
WARMER THAN AVERAGE WITH PERSISTENT TROUGHING OVER THE AREA.
SECOND LOW MAY FORM FROM A DEEP-LAYERED TROUGH WITH A SURFACE
REFLECTION ALONG 15N53W 26N60W FORECAST TO SHIFT EASTWARD
SLOWLY.  WIDELY SCATTERED SHOWERS LIE FROM 16N-27N BETWEEN
45W-57W NEAR THE TROUGH. UPPER SYSTEMS ALONG 39W AND 56W FORM A
DEEP TROUGH COVERING THE CENTRAL ATLC BETWEEN 25W-65W N OF 25N
WITH ITCZ ACTIVITY LIMITED TO THE E ATLC WITH LOTS OF DRY AIR
ALOFT.  IN THE E ATLC... UPPER MOISTURE IS LIMITED TO S OF 23N E
OF 29W WITH UPPER RIDGING IN PLACE SAVE DRY CYCLONIC FLOW FROM A
MID/UPPER CYCLONE OVER SOUTHERN MOROCCO.

$$
BLAKE


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