000
AXPZ20 KNHC 210926
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC FRI AUG 21 2009

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.

...TROPICAL WAVES...

TROPICAL WAVE IS ALONG 99W N OF 08N MOVING W 15 KT. SHORTWAVE IR 
SATELLITE IMAGES SHOW A BROAD AND ELONGATED AREA OF LOW TO 
MID-LEVEL CYCLONIC TURNING ASSOCIATED WITH THIS FEATURE. TOTAL 
PRECIPITABLE WATER IMAGES REVEAL A LARGE ZONE OF HIGHLY MOIST 
CONDITIONS...BUT STILL SHOW SOME EVIDENCE OF A MOISTURE MAXIMUM 
NEAR THE ANALYZED POSITION. SCATTEROMETER/MODEL DATA SUGGEST A 
200-300 NM SWATH OF E-SE 20 KT WINDS E OF THE AXIS...DUE TO THE 
PRESSURE GRADIENT BETWEEN IT AND RIDGING OVER THE GULF OF 
MEXICO. CONVECTION IS LIMITED AND MAINLY CONFINED TO THE 
INTERSECTION OF THE ITCZ. 

TROPICAL WAVE IS ALONG 118W FROM 09N TO 17N MOVING W 10 KT. THIS 
WAVE'S STRUCTURE IS SIMILAR TO THE ONE ALONG 99W. BROAD LOW TO 
MID-LEVEL CYCLONIC TURNING...COVERING 8 TO 10 DEGREES OF 
LONGITUDE...IS APPARENT ON SATELLITE IMAGES AND TO SOME DEGREE 
IN AN EARLIER QUIKSCAT PASS. A SMALL AREA OF SCATTERED MODERATE 
CONVECTION EXISTS NEAR THE N PORTION OF THE WAVE FROM 15N-17N 
BETWEEN 116W-119W. A MUCH LARGER ZONE LIES WITHIN THE 
INTERSECTION OF THE ITCZ. 

TROPICAL WAVE IS ALONG 132W FROM 09N TO 17N MOVING W 10 KT. A 
1009 MB LOW IS ALONG THE WAVE AXIS NEAR 14N. A SMALL CURVED BAND 
FEATURE HAS DEVELOPED NEAR AND W OF THE LOW CENTER. A HI-RES 
QSCAT PASS SHOWS EVIDENCE OF A NEARLY CLOSED WIND CIRCULATION 
AND A BROAD ZONE OF NE 20 KT WINDS N OF THE LOW...DUE TO THE  
PRESSURE GRADIENT BETWEEN THE LOW AND THE SUBTROPICAL RIDGE. 
SOME SLOW DEVELOPMENT IS POSSIBLE OVER THE NEXT COUPLE OF DAYS.

...ITCZ...
ITCZ AXIS IS CENTERED ALONG 09N79W TO 13N97W TO 12N125W TO 
10N140W. SCATTERED MODERATE CONVECTION IS WITHIN 150 NM S OF 
AXIS E OF 84W. SCATTERED MODERATE CONVECTION IS FROM 08N TO 13N 
BETWEEN 102W AND 126W. SCATTERED MODERATE ISOLATED STRONG 
CONVECTION IS FROM 08N TO 15N W OF 130W.

...DISCUSSION...

N OF 20N...
A FAIRLY COMPLEX MID-UPPER PATTERN IS IN PLACE ACROSS THE 
SUBTROPICS. AN UPPER HIGH IS OVER SRN MEXICO...AN UPPER LOW OFF 
THE SRN CALIFORNIA COAST...ANOTHER UPPER HIGH NEAR 22N132W AND 
ANOTHER UPPER LOW NEAR 22N142W. WHILE THE PATTERN IS 
COMPLEX...ONLY SENSIBLE WEATHER IS OVER MEXICO WHERE UPPER 
DIFFLUENCE AND LOW-LEVEL CONVERGENCE ASSOCIATED WITH LOCAL 
EFFECTS/DRAINAGE IS PRODUCING SCATTERED SHOWERS AND TSTMS FROM 
20N-28N BETWEEN 102W-107W AND OVER THE NRN GULF OF CALIFORNIA. A 
WEAK SFC TROUGH...ASSOCIATED WITH THE UPPER LOW OFF THE SRN 
CALIFORNIA COAST...HAS WEAKENED THE TRADES. THIS TROUGH WILL 
PERSIST FOR THE NEXT COUPLE OF DAYS ALLOWING WINDS TO BE MAINLY 
LESS THAN 20 KT...EXCEPT FOR NEAR THE N BAJA COAST.

S OF 20N...
ELY MID-UPPER FLOW AND A HIGHLY MOIST ENVIRONMENT EXIST ACROSS 
THE TROPICS. CONVECTION IS FOCUSED AROUND THE TROPICAL WAVES AND 
THE ITCZ. SEE ABOVE FOR MORE DETAILS. LONG PERIOD...15-18 
SECONDS...S TO SW SWELL IS PROPAGATING ACROSS MUCH OF THE AREA 
AND WILL CONTINUE FOR THE NEXT COUPLE OF DAYS. THIS WILL LIKELY 
CAUSE LARGE BREAKING WAVES ALONG THE COASTLINES OF CENTRAL 
AMERICA AND MEXICO. 
  
$$
CANGIALOSI