000
AXPZ20 KNHC 312104
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC FRI JUL 31 2009

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN
FROM THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
2000 UTC.

...TROPICAL WAVES...
TROPICAL WAVE FROM 04N-17N ALONG 105W MOVING W 15 KT.  SYSTEM 
HAS BEEN HOLDING TO ISOLATED CONVECTION IN SPITE OF NOT TOO 
FAVORABLE UPPER ENVIRONMENT.  MOST WEATHER IS WITHIN 180 NM W OF 
AXIS FROM 11N TO 13N.  WAVE IS APPROACHING AREA OF MORE BENIGN 
UPPER CONDITIONS WHICH COULD LIKELY LEAD TO INCREASED DEEP 
CONVECTION.  MODEL GUIDANCE PLACES 1011 MB LOW PRES CENTER IN 
VICINITY OF 111W WITHIN 24 HRS AND NEAR 115W WITHIN 48 HRS.   

TROPICAL WAVE FROM 04N-17N ALONG 124W MOVING W 15 KT.  SCATTERED 
MODERATE CONVECTION WITHIN 90 NM W OF WAVE AXIS FROM 08N-16N. 
WAVE APPROACHING MID-UPPER LEVEL CYCLONIC VORTEX WITH ABUNDANT 
MOISTURE AVAILABLE FOR CONVECTION...BUT STRONG NE SHEAR ON N 
HALF OF WAVE AXIS SHOULD DAMPEN ANY SIGNIFICANT DEVELOPMENT OF 
DEEP CONVECTION.  GUIDANCE SOLUTION DOES NOT APPEAR TO HAVE A 
GOOD HANDLE ON WHETHER CYCLONIC ORGANIZATION IS WARRANTED...BUT 
IF ANYTHING DOES DEVELOP IT IS LIKELY TO BE WELL AFTER 48 HRS 
WHEN THE UPPER CYCLONE EFFECTS ARE DIMINISHED.

...ITCZ...
AXIS ALONG 07N78W TO 09N98W TO 08N110W TO 11N123W TO 09N134W TO 
10N140W.  SCATTERED MODERATE CONVECTION WITHIN 180 NM OF AXIS 
FROM 90W-115W.  SCATTERED MODERATE CONVECTION WITHIN 150 NM S OF 
AXIS W OF 131W.

...DISCUSSION...
LASTING EFFECTS OF T.S. LANA STILL LINGER OVER FORECAST WATERS  
W OF 136W FROM 15N-18N AS FRESH NE WINDS ARE STILL NOTED...BUT 
EXPECTED TO DIMINISHED BY 24-30 HRS.  FURTHER INFORMATION ON 
T.S. LANA IN LATEST PUBLIC ADVISORY FROM CENTRAL PACIFIC 
HURRICANE CENTER UNDER AWIPS/WMO HEADERS MIATCPEP1/WTPZ31.

ELSEWHERE OVER N WATERS...SURFACE HIGH PRES CENTER 1028 MB AT 
35N146W HAS MODERATE TO STRONG SUBSIDENCE AND DRY STABLE AIR AT 
MID AND UPPER LEVELS W OF 120W.  RIDGE EXTENDS TO 20N110W SHOULD 
DRIFT W DURING NEXT 24 HRS EASING GRADIENT AS T.S. LANA MOVES W 
EFFECTIVELY DIMINISHING FRESH NE TRADES LEFT W OF 136W.  

FRESH BREEZE ACROSS GULF OF PAPAGAYO DIMINISHES WITH PASSAGE OF 
TROPICAL WAVE ENTERING E PAC...BUT REESTABLISHES IT AGAIN WITHIN 
48 HRS ONCE WAVE AXIS MOVES W AND STRONG BREEZE DOMINATES WRN 
CARIBBEAN.

CROSS EQUATORIAL SW SWELLS WITH SIGNIFICANT WAVE HEIGHTS TO 8 FT 
ENTER SOUTHERN CENTRAL SECTION OF BASIN AND EXPANDS TO S OF 10N 
BY END OF FORECAST PERIOD.

$$
WALLY BARNES