000 AXPZ20 KNHC 041600 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1605 UTC SAT JUL 04 2009 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 1500 UTC. ...TROPICAL WAVE... A TROPICAL WAVE IS ALONG 87W N OF 04N MOVING W 15-20 KT. THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. HOWEVER...THE WAVE IS NOT PARTICULARLY WELL-DEFINED AS FAR AS THE LOW LEVEL WIND FIELD IS CONCERNED BASED ON THE QUIKSCAT PASS AROUND 04/1145 UTC...WITH STRONG NE TO E GAP WINDS IN THE GULF OF PAPAGAYO... AND CROSS EQUATORIAL SOUTHWESTERLY FLOW OF 5 TO 10 KT ACROSS THE S HALF OF THE WAVE. THE POSITION OF THE WAVE IS BASED ON CONTINUITY FROM PREVIOUS POSITIONS. THIS WAVE IS EMBEDDED WITHIN THE ITCZ...AND ANY DEEP CONVECTION NEAR THE WAVE IS LIKELY BEING DRIVEN BY LOW LEVEL CONVERGENCE NEAR THE ITCZ. A TROPICAL WAVE IS ALONG 117W/118W FROM 06N TO 17N MOVING W NEAR 15 KT. THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM CIMSS. RECENT SATELLITE IMAGERY INDICATES THAT THIS WAVE COINCIDES WITH AN INVERTED-V PATTERN IN THE COVERAGE OF LOW LEVEL CLOUDS. THIS WAVE IS EMBEDDED WITHIN THE ITCZ...AND ANY DEEP CONVECTION NEAR THE WAVE IS LIKELY BEING DRIVEN BY LOW LEVEL CONVERGENCE NEAR THE ITCZ. ...ITCZ... ITCZ AXIS IS CENTERED ALONG 09N84W TO 10N94W TO 12N100W AND THEN FROM 11N106W TO 10N120W TO 07N140W. SCATTERED MODERATE CONVECTION IS N OF 03N BETWEEN 77W AND 84W. SCATTERED MODERATE CONVECTION IS N OF 9N BETWEEN 86W AND 88W. SCATTERED MODERATE TO STRONG CONVECTION IS N OF 09N BETWEEN 93W AND 111W. SCATTERED MODERATE CONVECTION IS FROM 06N TO 09N BETWEEN 101W AND 114W. SCATTERED MODERATE CONVECTION IS FROM 09N TO 12N BETWEEN 119W AND 125W. ...DISCUSSION... THE MAIN FORECAST CONCERN ACROSS THE TROPICS WILL BE THE DEVELOPMENT OF A SURFACE LOW ALONG A TROUGH CURRENTLY ANALYZED FROM 16N104W TO 10N103W MOVING W 10 KT...SEVERAL HUNDRED MILES SW OF ACAPULCO MEXICO. CONVECTION ASSOCIATED WITH THIS TROUGH IS LARGELY DISORGANIZED AT PRESENT AS IT INTERACTS WITH RELATIVELY STRONG CLOUD-LAYER VERTICAL WIND SHEAR. THIS SHEAR IS BEING DRIVEN BY THE DEEP LAYER HEIGHT GRADIENT BETWEEN A QUASI-STATIONARY DEEP-LAYER WARM-CORE HIGH OVER NW MEXICO AND A LOWER HEIGHTS TO THE SOUTH. AT THE SAME TIME...CROSS EQUATORIAL SOUTHERLY FLOW IS INTERACTING WITH THE INCREASING E TO SE LOW LEVEL FLOW S OF THE RIDGE TO RESULT IN AN AREA OF INCREASED LOW-LEVEL CYCLONIC VORTICITY WELL OFF THE MEXICAN COAST DURING THE NEXT 48 HOURS. GLOBAL MODEL GUIDANCE HAS BEEN TOO AGGRESSIVE IN SPINNING UP A LOW ALONG THE TROUGH...BASED ON CURRENT OBSERVATIONS. THE OPERATIONAL GFS HAS BACKED OFF CONSIDERABLY IN THE DEVELOPMENT OF THIS SYSTEM...WHILE OTHER AVAILABLE GUIDANCE APPEARS TO BE INITIALIZING WITH TOO STRONG OF A SYSTEM. THUS THE FORECAST WILL CLOSELY FOLLOW THE OPERATIONAL GFS...WHICH INDICATES A WEAK 1010 MB LOW ALONG THE TROUGH NEAR 16N107W IN A DAY OR SO. THE STRONGEST WINDS...IN THE 20-25 KT RANGE...WILL BE FOUND IN THE NE QUADRANT OUT TO 300 NM OR SO...WHERE LOCAL TOPOGRAPHIC VARIATIONS NEAR THE COAST OF MEXICO WILL ENHANCE BOUNDARY LAYER FLOW. THEREAFTER...THE TRACK/INTENSITY FORECASTS ARE HIGHLY UNCERTAIN...WITH A NUMBER OF MODELS GENEROUSLY STRENGTHENING THIS SYSTEM...AND THE GFS DOING SO MOST CONSERVATIVELY. ONE ARGUMENT CAN BE MADE THAT WEAKENING OF THE AFOREMENTIONED RIDGE BY EARLY NEXT WEEK...DRIVEN BY HEIGHT FALLS WITH THE APPROACH OF A LONGWAVE TROUGH...WILL LESSEN THE DEEP LAYER SHEAR SOMEWHAT THUS INCREASING THE THREAT FOR CONVECTIVE ORGANIZATION AND SURFACE PRESSURE FALLS. IF THIS SCENARIO PLAYS IT...IT WOULD MOST LIKELY BE MON/TUE...THOUGH LITTLE CONFIDENCE CURRENTLY EXISTS IN THE IMPACT OF THE PLACEMENT AND INTENSITY OF THE RESULTING SHEAR. NEVERTHELESS...20-25 KT WINDS WILL FOLLOW THE LOW IN ITS NE QUADRANT OUT TO 300 NM THROUGH EARLY NEXT WEEK AS IT IS STEERED TO THE W OR NW. ALSO...MODERATE EASTERLY LOW/MID-LEVEL FLOW S OF THE AFOREMENTIONED RIDGE OVER THE W CARIBBEAN WILL CONTINUE BLEEDING INTO THE GULF OF PAPAGAYO...WITH SURFACE WINDS BEING ACCELERATED INTO THE 20-30 KT RANGE NEAR AND DOWNSTREAM OF THE GULF OF PAPAGAYO...AS CONFIRMED BY THE HIGH RESOLUTION QUIKSCAT PASS AROUND 04/1145 UTC. THESE WINDS ARE LIKELY AT THEIR PEAK... WITH THE COVERAGE AND INTENSITY OF THESE GAP WINDS DECREASING DURING THE NEXT FEW DAYS AS THE UPPER RIDGE WEAKENS. SEAS UP TO 10 FT WILL BE FOUND IN THE GULF OF PAPAGAYO DRIVEN BY THESE STRONG WINDS. STRONG SOUTHERN HEMISPHERIC STORMS ARE ALSO SENDING LONG-PERIOD SOUTHWESTERLY SWELL NORTHWARD...WITH WAVE HEIGHTS OF 8 TO 10 FT COVERING A LARGE PART OF THE AREA S OF 15N E OF 116W BY LATE SUNDAY...BRINGING LARGE BATTERING WAVES TO THE SW COAST OF MEXICO BY SUN INTO EARLY NEXT WEEK. ALSO...A BRIEF PERIOD OF 20-25 KT WINDS DRIVEN BY THE SURFACE PRESSURE GRADIENT S OF A SURFACE RIDGE OVER MEXICO WAS PRESENT IN THE GULF OF TEHUANTEPEC BASED ON THE QUIKSCAT PASS AROUND 04/1145 UTC. AS THE SURFACE HIGH WEAKENS DURING THE NEXT DAY...THESE WINDS WILL QUICKLY DIMINISH. NE TO E WINDS OF 10 TO 15 KT COVER WESTERN PORTIONS OF THE AREA S OF A SURFACE RIDGE ALONG 28N W OF 117W N OF 10N. A FEW WEEK TROUGHS IN THE ITCZ WILL MOVE WESTWARD OCCASIONALLY INCREASING WINDS TO 20 KT ACROSS THIS AREA OF TRADES DURING THE NEXT COUPLE DAYS LOCALLY. A STRONGER W/E-ORIENTED RIDGE IS NOT BEING SUPPORTED AS A BROAD UPPER LEVEL TROUGH BECOMES SITUATED OVER THE N PORTION OF THE AREA. THUS...STRONGER TRADE WINDS ARE NOT CURRENTLY FORECAST. $$ COHEN