Eastern Pacific Tropical Weather Discussion

000
AXPZ20 KNHC 280927
TWDEP 

TROPICAL WEATHER DISCUSSION                                   
NWS NATIONAL HURRICANE CENTER MIAMI FL                       
1005 UTC MON JUL 28 2014

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 
0830 UTC.

...SPECIAL FEATURES...                                   
TROPICAL STORM HERNAN WAS DOWNGRADED FROM A HURRICANE CENTERED 
NEAR 19.9N 114.5W AT 28/0900 UTC OR ABOUT 315 NM SW OF THE 
SOUTHERN TIP OF BAJA CALIFORNIA MOVING WNW AT 13 KT. ESTIMATED 
MINIMUM CENTRAL PRESSURE IS 994 MB. MAXIMUM SUSTAINED WIND SPEED 
IS 60 KT WITH GUSTS TO 75 KT. HERNAN IS IN AN AREA OF NW 
SHEAR...WITH SCATTERED MODERATE TO STRONG CONVECTION EXTENDING 
60 NM IN THE SE QUADRANT OF THE CENTER OF HERNAN. SEE LATEST NHC 
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP3/WTPZ23 KNHC 
FOR MORE DETAILS.

...TROPICAL WAVES...                                      
TROPICAL WAVE IS OBSERVED BETWEEN 100W AND 105W FROM 08N TO 16N 
MOVING E AT 15-20 KT. SCATTERED MODERATE CONVECTION IS OBSERVED 
FROM 10N TO 16N BETWEEN 96W AND 102W. THIS WAVE IS EXPECTED TO 
PASS 110W EARLY TUE...THEN DEVELOP A WEAK LOW PRES AREA ON ITS 
SOUTHERN END NEAR THE ITCZ NEAR 115W BY EARLY WED.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...           
THE MONSOON TROUGH EXTENDS FROM 08N78W TO 09N85W TO 07N100W TO 
08N110W THEN RESUMES FROM 1011 MB LOW PRES NEAR 11N123W TO 
10N132W. SCATTERED MODERATE CONVECTION NOTED WITHIN 60 NM OF 
AXIS BETWEEN 80W AND 85W.

...DISCUSSION...                                                
AN UPPER LEVEL TROUGH IS NOTED ON WATER VAPOR IMAGERY WITH AXIS 
EXTENDING FROM 29N130W TO A BASE NEAR 15N130W. THIS IS 
DELIVERING DEEP LAYER DRY AIR OVER MUCH OF THE AREA W OF 125W. 
WHILE NO SIGNIFICANT CONVECTION REMAINS NEAR A 1008 MB SURFACE 
LOW NEAR 14N135W...AN ASCAT SATELLITE PASS FROM 0545 UTC 
INDICATED FRESH TO STRONG WINDS PERSIST WITHIN 300 NM IN THE 
NORTHERN QUADRANT OF THE LOW...BETWEEN THE LOW PRES AND THE 
SUBTROPICAL RIDGE N OF THE AREA. A PAIR OF ALTIMETER SATELLITE 
PASSES ALSO INDICATED SEAS OF 8 TO 11 FT IN THIS AREA OF 
ENHANCED TRADES. THE FORECAST CALLS FOR THE LOW TO WEAKEN AND 
THE WINDS TO DIMINISH THROUGH EARLY TUE AS THE LOW PRES CENTER 
MOVES W OF 140W...BUT WITH RESIDUAL SEAS TO 9 FT.

CONVECTION ACCOMPANYING THE 1011 MB LOW PRES ALONG THE ITCZ NEAR 
11N123W HAD BEEN FAIRLY ACTIVE OVER THE LAST COUPLE OF DAYS 
WHILE STILL FAR ENOUGH EAST OF THE BASE OF THE UPPER TROUGH AXIS 
TO BENEFIT FROM THE ASSOCIATED UPPER LIFT. THE CONVECTION HAS 
DIMINISHED SUBSTANTIALLY IN THE PAST 12 TO 24 HOURS HOWEVER AS 
THE LOW PRES ENCOUNTERS THE DRY AIR. 

SIMILARLY HERNAN IS STARTING TO WEAKEN AS IT ENTERS AN AREA OF 
SHEAR AHEAD OF THE UPPER TROUGH...ALONG WITH MORE STABLE AIR AND 
COOLER SEA SURFACE TEMPERATURES. CONVECTION HAS DIMINISHED AS 
WELL NEAR HERNAN AND IS SHEARING THE SE OF THE STORM CENTER. 

AN UPPER CYCLONE IS CENTERED OVER S CENTRAL MEXICO...ENHANCING 
CONVECTION NEAR THE TROPICAL WAVE BETWEEN 100W AND 105W. 
CONVECTIVE CELLS THAT WERE ACTIVE EARLIER IN THE EVENING NEAR 
12N100W HAVE LARGELY DIMINISHED...BUT NEW CONVECTION IS POPPING 
ALONG THE COAST OF MEXICO BETWEEN ACAPULCO AND MANZANILLO IN THE 
WAKE OF THE TROPICAL WAVE. 

$$ 
CHRISTENSEN