000
AXPZ20 KNHC 010312
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC THU JAN 01 2009

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

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0300 UTC.

...ITCZ...
THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE...05N78W TO 
04N82W TO 07N90W TO 09N110W TO 08N120W TO 09N140W. SCATTERED TO 
NUMEROUS MODERATE CONVECTION WITH ISOLATED STRONG CONVECTION 
WILL CONTINUE TO PROPAGATE WESTWARD DURING THE NEXT 12 HOURS 
WITHIN 120 NM N AND 90 NM S OF ITCZ BETWEEN 103W AND 120W. THIS 
WEATHER IS ASSOCIATED WITH TWO EASTERLY WAVES...ONE ALONG 118W 
AND THE OTHER ALONG 108W. SCATTERED MODERATE CONVECTION WITH 
ISOLATED STRONG CONVECTION WILL GRADUALLY DIMINISH IN AREAL 
COVERAGE DURING THE NEXT 12 HOURS FROM 07N TO 12N AND W OF 135W. 
THIS WEATHER WAS ASSOCIATED WITH MOISTURE AND LOW LEVEL 
INSTABILITY TRAILING BEHIND AN EASTERLY WAVE ALONG 142W. 

...DISCUSSION...
A MID LATITUDE UPPER LEVEL RIDGE WAS LOCATED NW OF THE AREA 
ALONG 145W. DOWNSTREAM...A SHORT WAVE TROUGH WAS MOVING SE 
ACROSS 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 ACROSS THE FORECAST AREA WAS ASSOCIATED WITH 
THIS TROUGH AS DRY STABLE LOW LEVEL AIR GENERALLY RESIDES TO THE 
IMMEDIATE E AND SE OF THIS FEATURE. 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 ALONG 140W...AND HAVE 
BEEN ACTING TO VENTILATE A LARGE AREA OF MODERATE TO DEEP 
CONVECTION ASSOCIATED WITH THE EASTERLY WAVE THAT HAS MOVED TO 
142W THIS EVENING. DYNAMICS ASSOCIATED WITH A SHORT WAVE TROUGH 
ROTATING AROUND THE BASE OF AN UPPER LEVEL TROUGH WELL WEST OF 
THE AREA...WILL LIFT TO THE NE DURING THE SHORT TERM...WITH 
WIDESPREAD CONVECTION THERE GRADUALLY DIMINISHING. THE OTHER 
EASTERLY WAVES ALONG 118W AND 108W WILL REMAIN ACTIVE DURING THE 
NEXT 12 HOURS AS ABUNDANT TRAILING MOISTURE REMAINS UNDER 
PERSISTENT 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 MERGING SEAS OF 8 TO 11 FT THIS 
EVENING IN STEEP EASTERLY WIND WAVES AND LONG PERIOD NORTHWEST 
SWELL. 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 108W...AND S OF 
15N...WHERE SEAS WERE RUNNING 8 TO 9 FT.

GAP WINDS ARE EXPECTED TO BEGIN TO INCREASE OVERNIGHT THROUGH 
THURSDAY MORNING...AND BRIEFLY REACH GALE FORCE IN THE GULF OF 
TEHUANTEPEC REGION...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.

SCATTERED TRADE WIND SHOWERS ARE EXPECTED OVERNIGHT ACROSS 
CENTRAL AMERICA...PRIMARILY ALONG THE NORTH AND EASTERN SLOPES 
OF THE MOUNTAINS.

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

$$
STRIPLING