000 AXPZ20 KNHC 280922 TWDEP TROPICAL WEATHER DISCUSSION NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 1005 UTC MON APR 28 2008 TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM THE EQUATOR TO 32N...EAST OF 140W. BASED ON 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 0900 UTC. ...ITCZ... ITCZ AXIS RUNS FROM 06N78W TO 05N90W TO 04N100W TO 06N120W TO 02N140W. SCATTERED MODERATE CONVECTION WITHIN 300 NM S OF AXIS BETWEEN 89W AND 99W. SCATTERED MODERATE AND EMBEDDED STRONG CONVECTION WITHIN 240 NM S OF AXIS BETWEEN 101W AND 107W. SCATTERED MODERATE CONVECTION WITHIN 210 NM N OF AXIS FROM 112W AND 125W. SCATTERED MODERATE CONVECTION BETWEEN 210 AND 240 NM N OF AXIS BETWEEN 125W AND 130W. ...DISCUSSION... E OF 110W... A DEEP TROUGH EXTENDING FROM THE EAST CENTRAL CONUS THROUGH NORTHERN MEXICO IS DRIVING A HEALTHY LATE APRIL COLD FRONT THROUGH THE NW GULF OF MEXICO THIS MORNING. MODELS INDICATE THE FRONT SHOULD SURGE SOUTHWARD ALONG THE FRONT RANGE OF THE SIERRA MADRE ORIENTAL AND THROUGH THE ISTHMUS OF TEHUANTEPEC DURING THE NEXT 24 HOURS. AFTER ITS PASSAGE...GUIDANCE CONTINUES TO FORECAST A SOMEWHAT RARE...LATE SEASON GALE OVER THE GULF OF TEHUANTEPEC. AS IS NORMALLY THE CASE...STRONG WINDS...THOUGH NOT TO GALE FORCE...SHOULD EXTEND WELL TO THE SW...WITH EFFECTS LIKELY AS FAR AS 300 NM DOWNSTREAM. HOWEVER...THE PROGRESSIVE NATURE OF THE CONUS TROUGH SHOULD RENDER THIS A RATHER SHORT- LIVED GAP WIND EVENT...AS WINDS ARE EXPECTED TO DROP TO BELOW GALE FORCE JUST AFTER 18 HOURS OF ITS ONSET. OF NOTE...THE BRIEF NATURE OF THE EVENT MEANS THAT SEAS WILL NOT HAVE A CHANCE TO BECOME FULLY DEVELOPED. STILL THOUGH...SEAS COULD BUILD TO AS HIGH 10 FT OVER A SMALL AREA...WITH A LARGER AREA OF 6 FT OR GREATER SEAS WITHIN ABOUT 75 NM EITHER SIDE OF A LINE FROM 16N95W TO 11N98W. OTHERWISE...A PLUME OF MOSTLY HIGH-LEVEL MOISTURE IS STREAMING FROM THE TROPICAL EASTERN PACIFIC ACROSS MEXICO TO THE U.S. GULF COAST AHEAD OF THE EAST CENTRAL CONUS TROUGH. STRONG UPPER-LEVEL DIVERGENCE...A GREATER INFLUX OF LOW-LEVEL MOISTURE...AND AN INCREASINGLY UNSTABLE ATMOSPHERE AHEAD OF THIS FEATURE HAVE HELPED IGNITE SCATTERED CONVECTION ALONG THE SPINE OF THE SIERRA MADRE ORIENTAL...BUT THIS ACTIVITY HAS LARGELY BEEN DECREASING IN COVERAGE IN RECENT HOURS. ADDITIONAL...THOUGH STILL ISOLATED ...CONVECTION IS NOTED FORMING WITHIN 90 NM EITHER SIDE OF 13N97W...LIKELY A RESULT OF THE FAVORABLE CONDITIONS AHEAD OF THE DIGGING EAST CENTRAL CONUS TROUGH. MARINE-WISE...A BROAD CYCLONIC FLOW SURROUNDING MAINLAND MEXICO GIVES WAY TO FAIRLY LIGHT TRADES OVER THE REMAINDER OF THE WATERS E OF 110W. SEAS GENERALLY RANGE FROM 3 TO 6 FT...HIGHEST WELL TO THE SW...WITH LOWER SEAS NEAR SHORE AND AS IS TYPICAL IN THE GULF OF CALIFORNIA. SEAS ARE DOMINATED BY LONG PERIOD SW SWELL PROPAGATING OUT OF THE SOUTHERN HEMISPHERE. W OF 110W... A STRONG MID- TO UPPER-LEVEL RIDGE...WITH AN AXIS FROM 19N140W TO 28N120W...IS CURRENTLY BLOCKING A LARGE CLOSED CYCLONE OVER THE GULF OF ALASKA AND ITS ASSOCIATED TROUGH FROM DIGGING INTO THE TROPICAL EAST PACIFIC. AS A RESULT...THE SOUTHERN END OF THE ASSOCIATED COLD FRONT HAS BECOME STATIONARY OVER THE FAR NW PART OF THE AREA FROM AROUND 30N138.5W TO 29N140W. OVER THE NEXT FEW DAYS...THE GULF OF ALASKA SYSTEM IS FORECAST TO SPREAD INTO THE WESTERN CONUS ...WHILE RIDGING OVER THE TROPICAL EAST PACIFIC W OF 120W IS SQUASHED AND EVENTUALLY DISAPPEARS. SURFACE HIGH PRESSURE IN THE WAKE OF TROUGH NEAR 34N152W SHOULD STRENGTHEN AND GRADUALLY SHIFT E BETWEEN NOW AND WED...WHICH SHOULD KEEP TRADES TO 20 KT ACTIVE FROM AROUND 8N TO 24N BUT W OF 130W. SEAS OVER THIS AREA SHOULD BE AS HIGH 9 FT IN MIXED NW SWELL PROPAGATING OUT OF THE NORTH PACIFIC AND NE WIND WAVES. EVENTUALLY NW SWELL SHOULD COMBINE WITH LONGER PERIOD SW SWELL COMING OUT OF THE SOUTHERN HEMISPHERE. FARTHER EAST...THE PRESSURE GRADIENT BETWEEN LOW PRESSURE DEVELOPING OVER THE THE WESTERN CONUS EARLY THIS WEEK AND HIGH PRES NE OF HAWAII SHOULD FAVOR AN ENHANCED NORTHERLY FLOW GENERALLY N OF 25N E OF 128W. THE STRONG NORTHERLY FLOW OF UP TO 25 KT SHOULD CAUSE SEAS TO BUILD TO 8 OR 9 FT IN N WIND WAVES TODAY. HOWEVER...A WELL-DEFINED SWELL GROUP ASSOCIATED WITH A GALE CENTER NOW OVER THE WESTERN GULF OF ALASKA SHOULD PROPAGATE WELL SE BY THU...CAUSING SEAS TO BUILD TO 10 TO 13 FT OVER THIS SAME AREA BY THU. FINALLY...REAL-TIME NCEP RE-ANALYSIS DATA INDICATES THAT ANOMALOUS WESTERLY FLOW IS INCREASING ALONG THE EQUATOR AT UPPER-LEVELS...WITH ANOMALIES CURRENTLY ON THE ORDER OF 40- TO 70-KT. THESE WESTERLY WIND ANOMALIES ARE ASSOCIATED WITH STRONG TROPICAL CONVECTIVE FORCING COMING OUT OF THE EASTERN HEMISPHERE ...WITH A MEAN CENTER NOW NEAR 130E. INDICATIONS ARE THAT THIS FORCING SHOULD CONTINUE MOVING E THIS WEEK...LIKELY RESULTING IN A NOTICEABLE INCREASE IN CONVECTIVE ACTIVITY SPREADING FROM W TO E S OF 10N ACROSS THE BASIN BY NEXT WEEK. $$ KIMBERLAIN