000 AXPZ20 KNHC 280324 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 0405 UTC THU MAY 28 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 0315 UTC. ...TROPICAL WAVES... A TROPICAL WAVE IS ALONG 82W S OF 13N EXTENDING FROM THE SW CARIBBEAN TO S OF THE PANAMA-COSTA RICA BORDER. THE WAVE IS MOVING WESTWARD AT 15-20 KT...AND WILL MAKE FURTHER PROGRESS INTO THE E PACIFIC REGION DURING THE NEXT DAY. THIS WAVE IS ASSOCIATED WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. ALSO...CIMSS WAVETRAK PRODUCT INDICATES A MAXIMUM IN LOW LEVEL CYCLONIC CIRCULATION AROUND THE WAVE. THIS WAVE IS ASSOCIATED WITH SCATTERED MODERATE AND ISOLATED STRONG CONVECTION ACROSS COSTA RICA...WESTERN PORTIONS OF PANAMA...AND THE ADJACENT PACIFIC WATERS. THIS CONVECTION IS BEING ENHANCED BY LOW LEVEL CONVERGENCE NEAR THE ITCZ. ...ITCZ... THE ITCZ AXIS EXTENDS ALONG 09N79W TO 09N99W TO 09N111W TO 04N130W TO 04N140W. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS WITHIN 90 NM SW OF THE COAST OF CENTRAL AMERICA FROM 07N TO 13N. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS FROM 04N TO 08N BETWEEN 85W AND 92W. SCATTERED MODERATE AND ISOLATED STRONG CONVECTION IS FROM 06N TO 11N BETWEEN 94W AND 112W. SCATTERED MODERATE CONVECTION IS WITHIN 60 NM EITHER SIDE OF THE ITCZ BETWEEN 117W AND 130W. ...DISCUSSION... A SURFACE RIDGE EXTENDS SOUTHWARD INTO THE NORTHERN WATERS FROM A 1021 MB SURFACE HIGH N OF THE AREA NEAR 36N132W. THE SURFACE HIGH CONTINUES WEAKENING AS IT DRIFTS EASTWARD AND INTERACTS WITH ATMOSPHERIC LIFT ASSOCIATED WITH A MID/UPPER-LEVEL SHORTWAVE TROUGH. CORRESPONDINGLY...THE SURFACE PRESSURE GRADIENT S OF THE HIGH IS SUFFICIENTLY WEAK FOR NE TO E TRADE WINDS TO HAVE FALLEN BELOW 20 KT BASED ON THE ASCAT PASS AROUND 27/1915 UTC. WAVEWATCH OUTPUT INDICATES THAT SEAS HAVE SUBSIDED BELOW 8 FT IN THIS REGION AS WELL. THE AFOREMENTIONED TROUGH IS CURRENTLY N OF 28N BETWEEN 124W AND 130W...WITH INSTABILITY NEAR THE TROUGH SUPPORTING SCATTERED SHOWERS IN THIS AREA. HOWEVER...DEEP CONVECTION IN THIS REGION IS BEING SUPPRESSED BY SUBSIDENCE ASSOCIATED WITH THE SURFACE HIGH AND RIDGE. WHILE THE TRADE WINDS HAVE WEAKENED...THE SURFACE PRESSURE GRADIENT BETWEEN THE SURFACE RIDGE OVER THE N WATERS AND A SURFACE TROUGH OVER MEXICO IS RESULTING IN NW TO N WINDS OF 20 TO 25 KT FROM 20N TO 23N BETWEEN 108W AND 111W...WITH W TO NW WINDS TO 20 KT FROM 23N TO 27N WITHIN 120 NM W OF THE BAJA PENINSULA. COMPUTER MODEL GUIDANCE IS LIKELY UNDER-FORECASTING THESE WIND SPEEDS...PARTICULARLY THE SOUTHERN AREA...BASED ON COMPARISONS WITH RECENT SCATTEROMETER DATA. THE HIGH RESOLUTION QUIKSCAT PASS AROUND 27/1315 UTC AND HIGH RESOLUTION ASCAT PASS AROUND 27/1730 UTC INDICATED THAT WIND SPEEDS COULD HAVE LOCALLY REACHED 25 TO 30 KT IN THE SOUTHERN AREA...HIGHEST NEAR THE COAST OF BAJA CALIFORNIA. ADDITIONALLY...AT 28/0000 UTC THE SHIP WITH IDENTIFIER A8CG6 WAS REPORTING NW TO N WINDS OF 23 KT NEAR 21.5N109.5W. THESE WIND SPEEDS ARE 5-10 KT HIGHER THAN COMPUTER MODEL OUTPUT AND ARE BEING ENHANCED BY VARIATIONS IN TERRAIN ALONG THE COAST OF MEXICO. DURING THE NEXT TWO DAYS...THESE AREAS OF WINDS ARE FORECAST TO PERSIST IN NEARLY THE SAME AREAS WITH SIMILAR INTENSITIES. ADDITIONALLY...W TO NW WINDS OF 20 TO OCCASIONALLY 25 KT ARE FORECAST TO IMPACT AREAS FROM 16N TO 20N E OF 106W DURING THE NEXT TWO DAYS...WHERE W TO NW FLOW WILL BE ENHANCED BY NEARBY TERRAIN VARIATIONS. AT 28/0000 UTC THE SHIP WITH IDENTIFIER 3FSB4 WAS REPORTING W TO NW WINDS OF 18 KT AT 18.5N104.5W. A DEEP LAYER TROUGH CURRENTLY NW OF THE DISCUSSION AREA CONTINUES DIGGING SOUTHWARD AS AN UPPER LEVEL JET MAXIMUM DIVES SOUTHEASTWARD TOWARD THE TROUGH AXIS. AN ASSOCIATED COLD FRONT WILL ENTER FAR NW PORTIONS OF THE DISCUSSION AREA BY EARLY FRI...WITH SOUTHERLY WINDS INCREASING TO 20 KT AHEAD OF THE FRONT LATE THU ACROSS THE FAR NW WATERS. CONSENSUS AMONG GLOBAL MODELS IS THAT AN UPPER LOW WILL CUT OFF OVER THE SOUTHERN EXTENT OF THE TROUGH BY LATE SATURDAY N OF THE DISCUSSION AREA. THE FRONT WILL CORRESPONDINGLY WEAKEN BY EARLY IN THE WEEKEND WITH DEEP LOW PRESSURE REMAINING N OF THE AREA...AND WINDS OVER THE NW FORECAST WATERS DIMINISHING. HOWEVER...STRONG WINDS AROUND THE SURFACE LOW N OF THE AREA WILL RESULT IN SEAS OF 8 TO 11 FT IN NW SWELL ENTERING THE NW WATERS BY LATE FRI. CONVECTION ASSOCIATED WITH THE ITCZ IS BEING ENHANCED BY UPPER LEVEL DIVERGENCE NEAR TWO UPPER LEVEL TROPICAL RIDGES. THE WESTERN RIDGE IS FROM 01N TO 13N W OF 129W. UPPER LEVEL DIVERGENCE ASSOCIATED WITH THIS RIDGE IS SUPPORTING SCATTERED MODERATE CONVECTION FROM 10N TO 13N BETWEEN 129W AND 132W. THE EASTERN RIDGE IS FROM 04N TO 15N E OF 111W. ABUNDANT DEEP LAYER MOISTURE IS EMBEDDED WITHIN THE EASTERN RIDGE AND IS INTERACTING WITH THE TROPICAL WAVE ALONG 83W S OF 13N TO GENERATE CONVECTION OVER PORTIONS OF THE E PACIFIC REGION. TO THE S OF THE ITCZ...THE ASCAT PASSES AROUND 27/1600 UTC AND 27/1730 UTC DEPICTED S TO SW WINDS TO 20 KT FROM 04N TO 08N BETWEEN 100W AND 114W. THE GFS APPEARS TO DEPICT THIS AREA OF WINDS RATHER WELL...WITH WINDS IN THIS AREA DIMINISHING BELOW 20 KT DURING THE NEXT DAY. $$ COHEN