000
AXPZ20 KNHC 212146
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC WED APR 21 2010

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 
2000 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE WAS ANALYZED FROM 09N84W TO 
07N91W TO 07N100W TO 05N130W TO 04N140W. SCATTERED MODERATE WITH 
ISOLATED STRONG CONVECTION WAS WITHIN 45 NM N AND 75 NM S OF THE 
ITCZ AXIS BETWEEN 129W AND 132W AS WELL AS WITHIN 300 NM S OF 
THE ITCZ AXIS BETWEEN 117W AND 122W. SCATTERED MODERATE 
CONVECTION WAS ELSEWHERE WITHIN 180 NM EITHER SIDE OF THE ITCZ 
AXIS W OF 107W. SCATTERED MODERATE CONVECTION WAS WITHIN 240 NM 
S OF THE ITCZ AXIS E OF 93W. 

...DISCUSSION...

AN AMPLIFIED MID TO UPPER LEVEL TROUGH OVER THE AREA N OF 20N E 
OF 135W AND EXTENDING N ALONG THE W COAST OF THE U.S. WILL CUT 
OFF FROM THE NORTHERN STREAM AND DRIFT E THROUGH THE DESERT SW 
AND FOUR CORNERS REGION OVER THE NEXT TWO DAYS. THE 1720 ASCAT 
PASS SHOWED 20 TO 25 KT NW TO N WINDS OVER NE WATERS ASSOCIATED 
WITH THE STRONG PRES GRADIENT BETWEEN THIS TROUGH AND 1036 MB 
HIGH PRES NW OF THE AREA NEAR 35N146W. SIMILARLY...THE PRES 
GRADIENT S OF THE HIGH BETWEEN IT AND THE ITCZ HAS BROUGHT 
STRONG EASTERLY TRADE WINDS TO W WATERS ACCORDING TO THE 1902 
UTC ASCAT PASS. THE HIGH PRES SYSTEM IS FORECAST TO WEAKEN AS IT 
IS NUDGED EASTWARD OVER THE NEXT TWO DAYS BY A COLD FRONT 
PASSING OVER ITS NW EDGE. AS THE TROUGH OVER THE SW U.S. MOVES 
EAST THU...LOOK FOR THE STRONGEST PRES GRADIENT TO MOVE E AS 
WELL...SEPARATING THE STRONGEST WINDS FROM THE EASTERLY TRADES 
AND POSSIBLY BRINGING W WINDS TO 20 KT WITHIN THE RELATIVELY 
SMALL AREAS DOWNWIND OF MOUNTAIN PASSES IN THE NORTHERN GULF OF 
CALIFORNIA. WINDS ARE EXPECTED TO DROP BELOW 20 KT OFF THE BAJA 
AND IN THE GULF OF CALIFORNIA FRI AS THE PRES GRADIENT SLACKENS. 
HOWEVER...TRADE WINDS WILL REMAIN STRONG OVER W WATERS THROUGH 
THE FORECAST PERIOD.

STRONG MOISTURE CONVERGENCE ALONG THE ITCZ BETWEEN THE NE TRADES 
AND STRONG SE TRADES S OF THE EQUATOR HAS PROVIDED FUEL FOR 
CONVECTION W OF 107W. A 1008 MB SURFACE LOW EMBEDDED IN THE ITCZ 
AT 1800 UTC NEAR 05N126W AND A TROUGH TO ITS W FROM 08N131W TO 
02N132W HAVE FURTHER HELPED POOL LOW LEVEL MOISTURE. THESE 
FEATURES LIE UNDER AN AREA OF BROAD ANTICYCLONIC TURNING...THE 
CENTER OF WHICH IS FORECAST TO GRADUALLY SHIFT E OVER THE NEXT 
FEW DAYS. THIS AREA IS EXPECTED TO REMAIN CONVECTIVELY ACTIVE AS 
A RESULT. A 60 KT WEST-SOUTHWESTERLY UPPER JET THAT EXTENDS FROM 
10N130W INTO CENTRAL MEXICO IS TRANSPORTING THE MID TO UPPER 
LEVEL MOSITURE ASSOCIATED WITH THE ITCZ CONVECTION EASTWARD INTO 
MEXICO.  FARTHER E...CONVECTION IS NOTED ALONG AND N OF THE ITCZ 
E OF 93W TO THE COAST OF COSTA RICA. THIS CONVECTION LIES UNDER 
THE W EDGE OF AN UPPER RIDGE AXIS THAT EXTENDS INTO NORTHERN 
SOUTH AMERICA. THIS RIDGE AXIS WILL CONTRACT E AND BE REPLACED 
BY 20 TO 30 KT SOUTHERLY FLOW ALOFT BY THU ON THE EASTERN SIDE 
OF AN UPPER TROUGH BUILDING BETWEEN 90W-100W. THIS PATTERN ALOFT 
WILL DIMINISH THE DEEP CONVECTION CURRENTLY IN PLACE. THE UPPER 
TROUGH WILL CUT OFF A LOW S OF THE GALAPAGOS ON FRI AND ALLOW AN 
ANTICYCLONE TO BUILD OVER THE ITCZ BETWEEN 95W AND 
110W...INCREASING THE CHANCE OF CONVECTION.

$$
SCHAUER