000
AXPZ20 KNHC 311601
TWDEP 

TROPICAL WEATHER DISCUSSION    
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SUN JUL 31 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 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1530 UTC.

...SPECIAL FEATURES...
TROPICAL STORM EUGENE...THE FIFTH NAMED STORM OF THE 2011 
SEASON...WAS CENTERED NEAR 11.0N 100.5W AT 31/1500 MOVING WNW OR 
285 DEGREES AT 9 KT. ESTIMATED MINIMUM CENTRAL PRES IS 1004 MB. 
MAXIMUM SUSTAINED WINDS ARE NOW 35 KT WITH GUSTS TO 45 KT. DEEP 
CONVECTION HAS CONTINUED TO ORGANIZE NEAR THE CENTER OF EUGENE 
WHICH LIES UNDER DIFFLUENT FLOW ALOFT BETWEEN E-NE WINDS OVER 
AND N OF THE SYSTEM ON THE SOUTHERN EDGE OF AN UPPER RIDGE AND 
MORE NORTHERLY WINDS JUST TO ITS S. THE UPPER FLOW IS STRONG 
ENOUGH TO KEEP SOME SHEAR OVER THE SYSTEM. THE RIDGE TO ITS N 
WILL STEER THE SYSTEM W-NW OVER THE NEXT FEW DAYS AS IT 
GRADUALLY STRENGTHENS. THE OFFICIAL FORECAST CALLS FOR EUGENE TO 
GRADUALLY STRENGTHEN AND POSSIBLY BECOME A HURRICANE BY LATE 
TUE. SEE LATEST NHC PUBLIC ADVISORY UNDER AWIPS/WMO HEADERS 
TCPEP5/WTPZ35 KNHC AND THE FULL FORECAST/ADVISORY UNDER 
AWIPS/WMO HEADERS TCMEP5/WTPZ25 FOR MORE DETAILS.

...ITCZ/MONSOON TROUGH...
MONSOON TROUGH AXIS EXTENDS FROM 10N86W TO 13N91W TO 11N97W THEN 
CONTINUES FROM 10N105W TO 1008 MB LOW PRES NEAR 12N118W TO 
10N125W TO 09N140W. SCATTERED MODERATE ISOLATED STRONG WITHIN 
120 NM EITHER SIDE OF AXIS BETWEEN 118W AND 135W. SCATTERED 
MODERATE WITHIN 90-120 NM EITHER SIDE OF AXIS E OF 92W.

...DISCUSSION...
PERSISTENT NORTHERN STREAM TROUGHING ALOFT ALONG 130W HAS 
WEAKENED THE DEEP LAYER SUBTROPICAL RIDGE OVER THE EASTERN NORTH 
PACIFIC. THE SUBTROPICAL SURFACE HIGH IS DISPLACED NW OF ITS 
CLIMATOLOGICAL POSITION TO NEAR 38N154W AND THE SURFACE 
REFLECTION OF THE DEEP LAYER TROUGH LIES FROM 32N126W TO 
26N130W. THE PRES GRADIENT REMAINS TIGHT ENOUGH OVER NW WATERS 
BETWEEN THE SUBTROPICAL HIGH AND THE TROUGH TO SUPPORT FRESH NE 
WINDS. THESE WINDS WILL DIMINISH LATER TODAY AS THE DEEP LAYER 
TROUGH BEGINS TO WEAKEN AND THE SUBTROPICAL HIGH IS WEAKENED BY 
AN APPROACHING COLD FRONT WELL N OF THE AREA. THE SUBTROPICAL 
HIGH WILL MIGRATE SE OVER THE NEXT FEW DAYS...AND FRESH TRADES 
ARE EXPECTED TO RETURN TO FAR W WATERS OVERNIGHT MON NIGHT.

TO THE S OF THIS AMPLIFIED NORTHERN STREAM PATTERN LIES A STRING 
OF ANTICYCLONES NEAR 13N142W...23N120W...AND NE OF THE AREA OVER 
THE U.S. SOUTHERN PLAINS. RIDGING BETWEEN THE EASTERN TWO 
ANTICYCLONE IS GENERATING DIFFLUENT UPPER FLOW THAT IS ENHANCING 
THE SCATTERED MODERATE WITH ISOLATED STRONG CONVECTION WITHIN 
150 NM OF THE MEXICAN COAST FROM 19N TO 22N AND SCATTERED 
MODERATE IN THE GULF OF CALIFORNIA FROM 23N TO 27N. THE 
ANTICYCLONE NEAR 20N120W WILL BECOME ENGULFED IN THE 
ANTICYCLONIC FLOW AROUND THE U.S. SOUTHERN PLAINS UPPER HIGH 
LATER TODAY AND THE RIDGE AXIS WILL SHIFT N THROUGH WESTERN 
MEXICO. 

GAP WINDS...WINDS ARE BEING ENHANCED THROUGH THE GULF OF 
TEHUANTEPEC BY THE INCREASING PRES GRADIENT BETWEEN TROPICAL 
STORM EUGENE AND HIGHER PRES OVER THE GULF OF MEXICO. A MUCH 
EARLIER 0408 UTC ASCAT PASS SHOWED 20-25 KT N TO NE WINDS IN THE 
GULF OF TEHUANTEPEC. AN APPROACHING ATLANTIC TROPICAL WAVE ALONG 
87W WILL ALLOW NE WINDS TO FUNNEL THROUGH THE ISTHMUS OF 
TEHUANTEPEC AS IT APPROACHES THIS EVENING. THIS WAVE IS 
EXPECTED TO BECOME CAUGHT IN THE MONSOON FLOW MON AND DISSIPATE. 
WINDS WILL DIMINISH TO LESS THAN 20 KT WITHIN 36 HOURS AS EUGENE
MOVES AWAY FROM THE AREA.

$$
COBB