000
AXPZ20 KNHC 300948
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC SUN DEC 30 2007

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0945 UTC.
 
...ITCZ...
INTERTROPICAL CONVERGENCE ZONE AXIS ALONG 9N78W 9N86W 5N103W 
7N119W 7N140W. SCATTERED MODERATE CONVECTION IS OBSERVED WITHIN 
30 NM OF 6.5N 82.5W AND WITHIN 150 NM OF 7N97W. SCATTERED 
MODERATE CLUSTERS NOTED WITHIN 120 NM OF 6.5N96.5W AND WITHIN 
150 NM EITHER SIDE OF LINE 11N112W 7N140W.  

...DISCUSSION...
A LONGWAVE TROUGH CONTINUES TO DOMINATE CENTRAL N AMERICA WITH 
AN ASSOCIATED SHORTWAVE TROUGH EXTENDING SW INTO THE DISCUSSION 
AREA ALONG 32N101W 21N112W...WITH THE TROUGH THEN CONTINUING W 
AS A SHEAR AXIS ALONG 23N127W INTO AN UPPER CYCLONE CUTTING OFF 
NEAR 18N138W...WITH A TROUGH IN TURN EXTENDING SE TO A BASE JUST 
N OF THE ITCZ AT 10N131W. THIS TROUGH AXIS IS IDENTIFIED BY A 
BAND OF UPPER DRY AIR ROUGHLY WITH 150 NM EITHER SIDE OF ITS 
AXIS...AND ALSO WITHIN 240 NM OF THE CUT OFF LOW CENTER. TO THE
N OF THIS TROUGH...AN UPPER ANTICYCLONE IS CENTERED AT 32N131W 
WITH A RIDGE EXTENDING E TO A SHARP CREST AT 31N115W. UPPER 
LEVEL MOISTURE IS NOTED UNDER THE RIDGE...BUT APPEARS TO 
EVAPORATING WITH TIME.

A TROPICAL ANTICYCLONE CONTINUES OVER THE CENTRAL CARIBBEAN WITH 
ITS ENVELOPE OF ANTICYCLONIC FLOW EXTENDING W OVER THE 
DISCUSSION AREA E OF 100W...ROUGHLY ALONG A RIDGE EXTENDING W 
TO A SHARP CREST AT 10N109W. AN EMBEDDED UPPER CYCLONE IS ALSO 
NOTED WITHIN THE RIDGE NEAR 11N93W...AND IS DRIFTING W WITH TIME 
WHILE ENHANCING THE ITCZ CONVECTION NEAR 6.5N96.5W.  

CONVECTION ALONG THE E PAC ITCZ IS ENHANCED W OF THE AREA NEAR 
7N150W...WITH THE RESULTANT DEBRIS MOISTURE ADVECTED E INTO THE 
AREA ALONG A TROPICAL PLUME...OBSERVED WITHIN 150 NM EITHER SIDE 
OF LINE FROM 5N140W TO 10N125W WHERE THE MOISTURE FANS OUT OVER 
THE DISCUSSION AREA FROM 8N TO 20N BETWEEN 130W AND 110W. THE 
PLUME THEN NARROWS AGAIN AS IT MOVES NE ACROSS OLD MEXICO AND 
THE NW GULF OF MEXICO WHERE THE MOISTURE ATTRIBUTES TO A 
PRE-FRONTAL SQUALL LINE CURRENTLY OVER THE N CENTRAL GULF 
COASTAL PLAINS AND FURTHER E THE SE CONUS. 

AT THE LOW LEVELS...HIGH PRES DOMINATES THE AREA N OF THE ITCZ
W OF 110W WITH THE EASTERLY TRADES S OF THE RIDGE UNEXPECTEDLY 
STILL IN THE 20-30 KT RANGE...BUT EXPECTED TO RAPIDLY DIMINISH 
TO ABOUT 20 KT AS THE RIDGE WEAKENS IN ADVANCE OF A STRONG COLD 
FRONT THAT WILL DIP INTO THE NW CORNER TUE MORNING. THIS COD 
FRONT IS ACCOMPANIED BY A FRESH NW SWELL TRAIN THAT WILL DRIVE 
20 FT SEAS TO 30N135W AROUND SUNRISE THU.

GAP WINDS SURGING TO ABOUT 20 KNOTS WILL CONTINUE FOR ANOTHER 
DAY OR SO THROUGH IN AND DOWNSTREAM OF THE GULF OF PAPAGAYO... 
WITH SEAS EXPECTED TO MAX AT 7 FT THEN THE GRADIENT WILL TIGHTEN 
AGAIN SUPPORTING AT LEAST 25 KT. NLY WINDS WILL ALSO BEGIN TO 
SURGE THROUGH THE GULF OF TEHUANTEPEC GAP LATE MON AND GRADUALLY 
INCREASE TO GALE FORCE BY SUNRISE TUE. THESE NLY WINDS WILL 
CONTINUE TO INCREASE TO STORM FORCE BY SUNSET TUE AND FURTHER 
INCREASE TO MINIMAL HURRICANE FORCE JUST AFTER SUNRISE WED WITH 
SEAS TO BUILDING TO ABOUT 23 FT NEAR 13N96W SUNSET WED. 

NW WINDS IN THE GULF OF CALIFORNIA WILL FLUCTUATE AROUND 20 KT 
DURING THE NEXT 48 HOURS WITH SEAS MAXING AT 6-7 FT IN CENTRAL 
EXPOSED WATERS.

$$
NELSON