000
AXPZ20 KNHC 172205
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC WED DEC 17 2008

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

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2115 UTC.

...ITCZ...

INTERTROPICAL CONVERGENCE ZONE IS CENTERED ALONG...4N77W 6N87W
6N100W 10N110W 10N125W 6N134W 6N140W. SCATTERED MODERATE/ISOLATED
STRONG CONVECTION IS WITHIN 120 NM N OF THE AXIS BETWEEN 
123W-126W. SCATTERED MODERATE CONVECTION IS WITHIN 60 NM OF THE
AXIS BETWEEN 113W-116W. CONVECTION IS EXPECTED TO INCREASE E OF
129W.

...DISCUSSION...

LONGWAVE UPPER TROUGH EXTENDS FROM THE FAR NW U.S. SW THROUGH
TO CENTRAL CALIFORNIA WHERE AN UPPER LEVEL LOW MOVING NE IS 
CENTERED NEAR 35N121W...THEN CONTINUES SW INTO THE AREA SW 
THROUGH 32N123W TO 25N128W TO 20N133W AND FURTHER SW WHERE IT 
HAS ABSORBED A SECONDARY MID/UPPER TROUGH TO 10N136W. THE UPPER 
FLOW BEHIND THE TROUGH IS DEPICTED AS CONFLUENT ON WATER VAPOR 
IMAGERY. THIS ALLOWING FOR A COLD AIR MASS TO FUNNEL INTO THE 
BACK SIDE OF THE LONGWAVE TROUGH. THIS WILL MAINTAIN STRONG 
BAROCLINICITY WITH THE TROUGH MOVING EWD AT ABOUT 25 KT N OF 
23N. THE ASSOCIATED SURFACE COLD FRONT EXTENDS FROM A 1005 MB 
LOW OVER NORTHERN BAJA CALIFORNIA SW TO 26N120W TO 21N129W. IT 
IS MOVING E 20-25 KT. THE LOW IS FORECAST TO QUICKLY LIFT NE 
ACROSS THE WESTERN CONUS THROUGH THU MORNING AS THE UPPER LEVEL 
LOW OVER CENTRAL CALIFORNIA BECOMES ABSORBED BY THE NORTHERN 
PORTION OF THE LONGWAVE TROUGH OVER THE NW U.S. AND THE MAIN 
AREA OF FAVORABLE UPWARD LIFT EJECTS NE TO WELL NE OF THE NE 
PART OF THE AREA.

N WINDS OF 20-30 KT CAN BE EXPECTED TO THE N OF THE FRONT INTO
EARLY TONIGHT...BUT DIMINISH QUICKLY EARLY TONIGHT AND ON THU
AS THE FRONT DISSIPATES WITH LOSS OF ITS MAIN UPPER SUPPORT.
THE FRONT IS FORECAST TO DISSIPATE OVER THE FAR E PART OF THE
AREA OVER THE SUB-TROPICAL PACIFIC NEAR SOUTHERN BAJA CALIFORNIA 
IN ABOUT 36-48 HOURS. THE MAIN MARINE PROBLEM WILL BE RELATIVELY 
HIGH SEAS IN N SWELLS BEHIND THE FRONT THROUGH AT LEAST THU 
EVENING. SEAS UP TO 15 FT ARE INITIALLY BEING OBSERVED...BUT ARE 
FORECAST BY WAVEWATCH MODEL GUIDANCE TO SUBSIDE TO 12 FT BY THU 
AFTERNOON AND TO 9 FT OVER THE AREA FROM 20N-25N E OF 121W BY 
FRI AFTERNOON.

NE TRADE WINDS OF 20 TO 25 KT CONTINUE OVER AN AREA THAT OVERLAPS
THAT DESCRIBED BEHIND THE FRONT FROM 10N TO 25N W OF 125W. SEAS
HERE ARE IN THE RANGE OF 8-10 FT. THIS AREA OF NE TRADES IS 
EXPECTED TO GREATLY DIMINISH OVER THE NEXT COUPLE DAYS AS HIGH 
PRES RIDGING OVER THE WESTERN PORTION OF THE AREA BREAKS DOWN AS 
THE NEXT FRONTAL SYSTEM ENCROACHES INTO THE NW CORNER AS IT ALSO 
WEAKENS.

ADDITIONALLY...N TO NE GAP WINDS WINDS OF 20 TO 25 KT ARE 
FUNNELING INTO AND DOWNSTREAM OF THE GULFS OF PANAMA...PAPAGAYO 
AND TEHUANTEPEC AREAS...AND WILL GENERATE BUILDING SEAS TO 6 
FEET JUST OFFSHORE...INCREASING 6 TO 8 FEET FURTHER DOWNSTREAM. 

MARINE CONDITIONS ACROSS THE EQUATORIAL EASTERN PACIFIC W OF 85W 
WILL REMAIN SEASONABLE DURING THE NEXT 24 HOURS...WITH MODERATE 
S TO SE TRADE WINDS...AND A MIXTURE OF MODEST WIND WAVES AND 
MERGING LONG PERIOD SWELL ENERGY FROM BOTH HEMISPHERES.

WATER VAPOR IMAGERY AND CIMSS TPW PRODUCTS DEPICT LARGE POOLS OF 
MOISTURE OVER THE TROPICAL E PACIFIC E OF 140W...WITH WEAK 
EASTERLY WAVES ANALYZED SUGGESTED ALONG 113W AND 132W. 
ANTICYCLONIC SHEAR ASSOCIATED WITH THE AMPLIFIED UPPER TROUGH 
DISCUSSED ABOVE WILL CONTINUE TO PRODUCE VERY FAVORABLE 
VENTILATION AND UPPER DIVERGENCE DURING THE NEXT 12-24 HRS FOR 
ACTIVE ITCZ CONVECTION EAST OF THE UPPER TROUGH AXIS...AND MOST 
CONCENTRATED NEAR THESE WEAK EASTERLY PERTURBATIONS. 

$$
AGUIRRE