000 AXPZ20 KNHC 200951 TWDEP TROPICAL WEATHER DISCUSSION NWS NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC THU OCT 20 2011 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL ANALYSIS. BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0715 UTC. ...ITCZ/MONSOON TROUGH... THE MONSOON TROUGH AXIS WAS ANALYZED FROM 12N99W TO 13N110W TO 12N130W. ITCZ AXIS WAS ANALYZED FROM 12N130W TO 09N140W. SCATTERED MODERATE CONVECTION LIES WITHIN 60 NM N AND 75 NM S OF THE AXIS BETWEEN 112W AND 117W AS WELL AS N OF THE AXIS TO THE MEXICAN COAST BETWEEN 96W AND 102W N OF 11N. ...DISCUSSION... A STRONG COLD FRONT HAS MOVED THROUGH THE ISTHMUS OF TEHUANTEPEC...WITH NLY WINDS FUNNELING THROUGH THE CHIVELA PASS INTO THE GULF OF TEHUANTEPEC. SCATTERED MODERATE CONVECTION IS FOUND JUST S OF THE COLD FRONT THAT EXTENDS THROUGH GUATEMALA INTO THE AREA N OF 12N E OF 92W TO CENTRAL AMERICAN COAST. SHIP 9VVD REPORTED 30 KT WINDS DOWNSTREAM OF TEHUANTEPEC NEAR 14.3N 96.1W AT 0300 UTC. OBSERVATIONS AT SALINA CRUZ SHOWED THE N WINDS ACCELERATED FROM 20 KT FROM 0200-0400 UTC TO 25 KT BY 0500-0700 UTC AS EARLY MORNING DRAINAGE FLOW BEGAN TO ENHANCE THE WINDS THROUGH THE PASS. WHILE THERE ARE NO DIRECT OBSERVATIONS OF GALE FORCE WINDS...ALL SIGNS POINT TO A GALE WIND EVENT IN TEHUANTEPEC. WINDS ARE ESTIMATED TO BE AS STRONG AS 40 KT. A GALE WARNING IS IN EFFECT UNTIL THIS AFTERNOON WHEN THE DEEP LAYER TROUGHING OVER THE GULF OF MEXICO SWINGS NORTHEASTWARD AND WINDS IN THE SW GULF OF MEXICO WEAKEN. WINDS TO 30 KT WILL CONTINUE THROUGH THE REMAINDER OF THE FORECAST PERIOD WITH THE ASSISTANCE OF EARLY MORNING DRAINAGE FLOW AND THE PASSAGE OF A REINFORCING SPOKE IN THE DEEP LAYER TROUGH OVER THE GULF OF MEXICO ON FRI. A BROAD MID-LEVEL GYRE LIES OVER THE REGION FROM 07N TO 17N BETWEEN 97W AND 115W. CONVECTION ASSOCIATED WITH THIS GYRE HAS SHIFTED W AND DIMINISHED OVER THE PAST 24 HOURS...WITH 20 TO 25 KT OF E-NE SHEAR FOUND OVER THE SYSTEM. IN ADDITION TO THE CONVECTION NOTED NEAR THE MONSOON TROUGH IN THIS AREA... SCATTERED MODERATE CONVECTION WITH THE GYRE LIES FROM 07N TO 10N BETWEEN 107W AND 113W. CONDITIONS ALOFT SHOULD BECOME MORE DIFFLUENT OVER THE GYRE AS AN ANTICYCLONE CURRENTLY NEAR THE MOUTH OF THE GULF OF CALIFORNIA MOVES S TOWARD THE GYRE. THE FORECAST CALLS FOR A WEAK SURFACE REFLECTION OF THE GYRE TO DEVELOP TODAY THAT WILL DRIFT W ALONG THE MONSOON TROUGH THROUGH THE END OF THE PERIOD ON SAT MORNING. THE 0430 UTC ASCAT PASS SHOWED A CLOSED LOW LEVEL CIRCULATION TRYING TO FORM NEAR 12N102W WITH FRESH E-SE TO ITS NE. THESE WINDS ARE EXPECTED TO CONTINUE TODAY AS THE LOW FORMS AND THE PRES GRADIENT BETWEEN IT AND HIGH PRES OVER E CENTRAL MEXICO STRENGTHENS. WINDS WILL DIMINISH BY FRI AFTERNOON AS THE LOW MOVES W AND HIGH PRES WEAKENS. THE SUBTROPICAL HIGH NW OF THE FORECAST AREA HAS BEEN COMPROMISED BY WEAK TROUGHING ALOFT ALONG 135W AND A DEEP-LAYER TROUGH TO THE NW WITH AN ASSOCIATED COLD FRONT THAT EXTENDS AS CLOSE AS 33N145W. THE PRES GRADIENT BETWEEN THIS HIGH AND TROUGHING OVER NW MEXICO AT THE SURFACE CONTINUES TO SUPPORT A SMALL AREA OF FRESH N WINDS OVER CENTRAL FORECAST WATERS N OF 27N. THESE WINDS ARE EXPECTED TO DIMINISH LATER THIS MORNING AS THE HIGH PRES SHIFTS NW AND LOW PRES OVER NW MEXICO WEAKENS...WEAKENING THE PRES GRADIENT. THE COLD FRONT WILL DISSIPATE N OF THE AREA OVERNIGHT TONIGHT...ALLOWING THE SUBTROPICAL HIGH TO STRENGTHEN AND SHIFT E FRI. BY EARLY SAT...NE TRADE WINDS ARE EXPECTED TO RETURN TO CENTRAL WESTERN WATERS AS THE PRES GRADIENT BETWEEN THE SUBTROPICAL HIGH AND THE ITCZ INCREASES. $$ SCHAUER