000
AXPZ20 KNHC 180352
TWDEP 

TROPICAL WEATHER DISCUSSION    
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC WED MAR 18 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 
0230 UTC.

...ITCZ...
THE ITCZ AXIS LIES ALONG A LINE FROM 04N77W TO 05N93W TO 01N113W 
TO 09N140W. SCATTERED MODERATE CONVECTION IS WITHIN 90 NM S OF 
THE AXIS BETWEEN 83W AND 85W. NUMEROUS MODERATE CONVECTION IS 
FROM 05N TO 13N BETWEEN 121W AND 130W. SCATTERED MODERATE 
CONVECTION IS FROM 06N TO 10N W OF 133W.

...DISCUSSION...

THE UPPER LEVEL PATTERN FEATURES A ZONALLY-ELONGATED POLAR JET 
STREAM THAT EXTENDS FROM THE E PACIFIC REGION INTO THE NORTHERN 
ROCKIES OF THE CONUS. THE CORRESPONDING VERTICAL SHEAR IS 
ASSOCIATED WITH A STATIONARY FRONT THAT REMAINS WELL N OF THE 
DISCUSSION AREA. HOWEVER...THE UPPER LEVEL FLOW N OF THE REGION 
IS FORECAST TO AMPLIFY LATER THIS WEEK...AS A SHORTWAVE TROUGH 
CURRENTLY OVER THE GULF OF ALASKA DIVES SOUTHEASTWARD. IN 
RESPONSE...THE STATIONARY FRONT WILL BE FORCED SOUTHWARD BY 
FRIDAY...WITH A WEAKENING COLD FRONT APPROACHING THE 
NORTHWESTERN PORTION OF THE DISCUSSION AREA BY SATURDAY. WHILE 
THE WIND IMPACT WILL BE RELATIVELY MINIMAL...NORTHWESTERLY SWELL 
CONTAINING SEA HEIGHTS UP OVER 10 FT WILL APPROACH THE 
NORTHWESTERN WATERS BY SATURDAY. IN THE MEANTIME...NORTHWESTERLY 
SWELL WITH SEA HEIGHTS OF UP TO 11 FT CONTINUE TO DRIFT 
SOUTHEASTWARD ACROSS THE NORTHEASTERN HALF OF THE DISCUSSION 
AREA. THESE SEAS CONTINUE SUBSIDING AS THEY DEPART THEIR SOURCE 
REGION N OF THE AREA.

A 1028 MB SURFACE HIGH IS CENTERED N OF THE AREA NEAR 
33N132W...WITH THE ENHANCED SURFACE PRESSURE GRADIENT AT THE 
SOUTHERN PERIPHERY OF THIS FEATURE ENHANCING NE TO E TRADES 
ACROSS THE REGION. AN ASCAT PASS AROUND 17/1840 UTC SHOWED NE TO 
E WINDS OF 20 TO 25 KT FROM 07N TO 21N W OF 120W...WITH 
WAVEWATCH GUIDANCE INDICATED WAVES TO 10 FT IN THIS AREA. AS THE 
UPPER FLOW N OF THE AREA AMPLIFIES...THE SURFACE HIGH IS 
EXPECTED TO WEAKEN DURING THE NEXT FEW DAYS. IN RESPONSE...TRADE 
WINDS WILL SLACKEN...WITH SEAS GRADUALLY SUBSIDING.

AS FOR CONVECTIVE ACTIVITY...UPPER LEVEL DIFFLUENCE N OF THE 
ITCZ AXIS CONTINUES IS SUPPORTING THE CONVECTION ASSOCIATED WITH 
THE ITCZ W OF 121W. THE DIFFLUENCE IS EMBEDDED WITHIN AN UPPER 
TROUGH LOCATED S OF 18N W OF 110W. FARTHER TO THE E...DEEP LAYER 
DRY AIR AND STABLE ATMOSPHERIC CONDITIONS EMBEDDED WITHIN AN 
UPPER RIDGE ARE RESULTING IN FAIR WEATHER CONDITIONS. ALSO...THE 
REMNANT UPPER LOW NE OF HAWAII APPEARS TO BE MOSTLY DISCONNECTED 
WITH THE NORTHERN STREAM AND CONTINUES TO WEAKEN...WHILE THE 
CORRESPONDING SURFACE LOW NW OF THE AREA CONTINUES SPINNING DOWN 
AS WELL. UPPER LEVEL DIFFLUENCE E OF THE UPPER LEVEL TROUGH IS 
SUPPORTING SCATTERED MODERATE CONVECTION THAT HAS NOW MOVED N OF 
THE DISCUSSION AREA.

GAP WINDS...
SURFACE HIGH PRESSURE BUILDING SOUTHWARD OVER EASTERN MEXICO IN 
THE WAKE OF A FRONT OVER THE GULF OF MEXICO IS SUPPORTING A 
RELATIVELY STRONG SURFACE PRESSURE GRADIENT ACROSS THE ISTHMUS 
OF TEHUANTEPEC...WITH STRONG N TO NE WINDS FUNNELING INTO THE 
GULF OF TEHUANTEPEC. COMPUTER MODEL GUIDANCE INDICATES THAT 
WINDS IN THIS REGION HAVE DECREASED AFTER THE 1218 UTC HIGH 
RESOLUTION QUIKSCAT PASS THAT SHOWED INDICATED N TO NE WINDS OF 
30 TO 40 KT IN THE GULF OF TEHUANTEPEC. THIS IS IN RESPONSE TO 
THE FRONT OVER THE GULF WEAKENING...ALONG WITH WEAKENING OF THE 
SURFACE RIDGE N OF THE FRONT. THUS THE GALE WARNING FOR THE GULF 
OF TEHUANTEPEC HAS EXPIRED. ALSO...TRADE WINDS ACROSS THE 
CARIBBEAN CONTINUE WITH A PERSISTENT SURFACE LOW OVER NW 
COLOMBIA. THESE WINDS CONTINUE TO BLEED INTO THE GULFS OF PANAMA 
AND PAPAGAYO. GAP WINDS OF AROUND 20 KT IN THE GULFS OF 
TEHUANTEPEC AND PAPAGAYO ARE FORECAST TO CONTINUE PERIODICALLY 
DURING THE NEXT FEW DAYS...WITH THE STRONGEST WINDS EXPECTED 
LATE AT NIGHT WHEN DRAINAGE FLOW OFF HIGHER TERRAIN IS MAXIMIZED 
IN THE PRESENCE OF DEEP LAYER DRY AIR. HOWEVER...WINDS IN THE 
GULF OF PANAMA ARE EXPECTED TO REMAIN BELOW 20 KT IN ABOUT A 
DAY...WHEN THE SURFACE RIDGING OVER THE CARIBBEAN WEAKENS AND 
THE SURFACE LOW OVER NW COLOMBIA FILLS.

$$

COHEN