000
AXPZ20 KNHC 312224
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC WED DEC 31 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 
2130 UTC.

...ITCZ...
THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE...05N78W TO 
04N82W TO 07N90W TO 09N104W TO 08N110W TO 07N117W TO 08N125W TO 
08N140W. SCATTERED TO NUMEROUS MODERATE CONVECTION WITH ISOLATED 
STRONG CONVECTION WAS OCCURRING BEHIND AN EASTERLY WAVE ALONG 
118W...AND EXTENDED EASTWARD TO 104W...AND NORTHWARD TO 10.5N. 
THE CONVECTIVELY ACTIVE AREA SHOULD CONTINUE TO PROPAGATE 
WESTWARD AROUND 15 KT AS IT REMAINS UNDER DIFFLUENT FLOW ALOFT. 
ANOTHER EASTERLY WAVE HAS EXITED THE AREA TO THE WEST OF 
140W...WITH TRAILING MOISTURE YIELDING SCATTERED MODERATE 
CONVECTION WITH ISOLATED STRONG CONVECTION EASTWARD TO 135W. 
AMPLE TROPICAL MOISTURE BETWEEN 07N AND 15N AND BETWEEN 120W AND 
135W WAS YIELDING ISOLATED TO SCATTERED MODERATE CONVECTION. 

...DISCUSSION...
A MID LATITUDE UPPER LEVEL RIDGE WAS LOCATED JUST NW OF THE AREA 
ALONG 147W. DOWNSTREAM...A SHORT WAVE TROUGH WAS MOVING SE INTO 
CENTRAL CALIFORNIA...EXTENDING SW TO A MID LEVEL VORT CENTER 
NEAR 28N130W...WHICH WAS SINKING SLOWLY S...WITH A WEAK TROUGH 
CONTINUING SW TO NEAR 25N140W. THE SHORT WAVE IS FORECAST TO 
MOVE SE INTO THE DESERT SW OF THE U.S. DURING THE NEXT 24 
HOURS...WHILE DRAGGING THE SW EXTENSION OF THIS TROUGH SLOWLY 
SE. LITTLE WEATHER IS ASSOCIATED WITH THIS TROUGH. DEEP LAYERED 
HIGH PRESSURE WILL BUILD BEHIND THE TROUGH DURING THE NEXT 36 
HOURS AND ACT TO REINFORCE THE SURFACE HIGH PRESSURE RIDGE 
CURRENTLY IN PLACE ACROSS THE EASTERN PACIFIC. 

EQUATORIAL WESTERLIES ENTER THE AREA ALOFT...AND HAVE BEEN 
ACTING TO VENTILATE A LARGE AREA OF MODERATE TO DEEP CONVECTION 
ASSOCIATED WITH THE EASTERLY WAVE THAT HAS MOVED W OF 140W THIS 
AFTERNOON. THE OTHER EASTERLY WAVE ALONG 118W WILL REMAIN 
ACTIVE DURING THE NEXT 12 HOURS AS ABUNDANT MOISTURE TRAILING IT 
REMAINS UNDER DIFFLUENT WESTERLIES ALOFT.

A MODEST LOW LEVEL PRESSURE GRADIENT BETWEEN THE E PACIFIC HIGH 
AND THE WESTERN MOST WAVE IS MAINTAINING A BROAD ZONE OF NE 
WINDS OF 20 TO 25 KT...WITH SEAS 8 TO 11 FT EARLY THIS EVENING. 
SEAS ACROSS THIS AREA AND W OF 135 ARE FORECAST TO BUILD TO 12 
FT BY 24 HOURS. THIS ZONE OF FRESH NORTHEASTERLIES EXTENDED 
EASTWARD TO N OF THE WAVE ALONG 118W...AND S OF 15N...WHERE SEAS 
WERE RUNNING 8 TO 9 FT.

WEAK UPPER LEVEL DIVERGENCE E THROUGH SE OF THE MID TO UPPER VORT
MENTIONED ABOVE WAS VENTING ISOLATED AREAS OF MODERATE 
CONVECTION S OF 20N AND BETWEEN 128W AND 120W. 

GAP WINDS HAVE LESSENED TODAY TO AROUND 25 KT IN THE GULF OF 
TEHUANTEPEC REGION...BUT WILL INCREASE TO GALE FORCE BRIEFLY 
THURSDAY MORNING BEFORE FALLING TO LESS THAN 30 KT THURSDAY 
NIGHT. 

GAP WINDS WILL CONTINUE ACROSS AND DOWNWIND OF THE GULF OF 
PAPAGAYO REGION THROUGH AT LEAST THE NEXT 48 HOURS...AND MAY 
PEAK AT 25 TO 30 KT...WITH SEAS 9 FT...ON THURSDAY MORNING.

A STRONG PULSE OF SW SOUTHERN HEMI SWELL IS FORECAST TO IMPACT 
CENTRAL AMERICA BEYOND 48 HOURS.

$$
STRIPLING