000
AXPZ20 KNHC 172111
TWDEP 

TROPICAL WEATHER DISCUSSION      
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC MON SEP 17 2007

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 
2100 UTC.

...SPECIAL FEATURES...

AN AREA OF LOW PRES...ASSOCIATED WITH A TROPICAL WAVE...IS 
ANALYZED 1010 MB CENTERED NEAR 13N104W. SCATTERED SHOWERS AND 
TSTMS ARE MOSTLY ALIGNED LINEARLY NE-SW TO THE N AND W OF THE 
LOW-LEVEL CENTER FROM 12N-16N BETWEEN 103W-108W. AN EARLIER 
QSCAT PASS PARTIALLY CAPTURED THE CIRCULATION OF THIS SYSTEM. IT 
REVEALED SEVERAL UNCONTAMINATED 20 KT VECTORS TO THE E OF THE 
LOW. CONDITIONS APPEAR FAVORABLE FOR DEVELOPMENT...AND A 
TROPICAL DEPRESSION COULD FORM DURING THE NEXT COUPLE OF DAYS AS 
IT MOVES WESTWARD OR WEST-NORTHWESTWARD AT 10 KT.

...TROPICAL WAVES...

TROPICAL WAVE ALONG 116W FROM 8N TO 20N IS MOVING WWD 5-10 KT. 
THE WEAK LOW ALONG THE NRN PORTION OF THE WAVE HAS BEEN DROPPED 
FROM THE 18Z ANALYSIS AS THE LOW-LEVEL CU LINES NOW SUGGEST AN 
OPEN WAVE. ONLY ISOLATED TO SCATTERED SHOWERS AND TSTMS ARE 
WITHIN 120 NM W OF WAVE AXIS SHEARED BY MODERATE NE TO ELY UPPER 
FLOW. STRONGER MORE ORGANIZED CONVECTION IS W OF THE WAVE 
ALIGNED WITHIN THE ITCZ AND ENHANCED BY ANOTHER AREA OF LOW 
PRES...DISCUSSED BELOW.

...ITCZ...

ITCZ AXIS IS CENTERED ALONG 10N86W 8N95W 12N111W 16N122W 9N140W. 
BESIDES FOR CONVECTION ASSOCIATED WITH THE SPECIAL FEATURE 
...SCATTERED MODERATE IS WITHIN 120 NM OF AXIS BETWEEN 118W AND 
126W. ISOLATED MODERATE IS WITHIN 60 NM OF AXIS BETWEEN 131W AND 
134W AND W OF 138W.

...DISCUSSION...
AT THE SFC...MODERATE SUBTROPICAL RIDGING IS IN PLACE EXTENDING 
SW FROM A 1029 MB HIGH CENTER LOCATED NW OF THE AREA NEAR 
36N150W. IN ADDITION TO THE TROPICAL WAVES DISCUSSED ABOVE THERE 
IS ANOTHER AREA OF LOW PRES ALONG THE ITCZ ENHANCING TROUGHING 
ACROSS THE TROPICS. THIS SYSTEM IS CENTERED NEAR 14N128W 
ANALYZED 1012 MB. THE LOW-LEVEL CLOUD STRUCTURE IS FAIR ON VIS 
IMAGES BUT THE ASSOCIATED CONVECTION IS DISORGANIZED AND MOSTLY 
CONFINED TO THE INTERSECTION OF THE ITCZ. THE TIGHTENED PRES 
GRADIENT BETWEEN THE SUBTROPICAL HIGH AND LOWS ALONG THE ITCZ IS 
ENHANCING NE TRADES ACROSS THE W PORTION OF THE REGION. 

IN THE MID AND UPPER LEVELS...AN UPPER LOW IS DRIFTING NW 
CENTERED NEAR OUR NW CORNER NEAR 30N139W. A SHARP SHORTWAVE 
TROUGH EXTENDS SWD FROM THE WRN U.S. ACROSS NW MEXICO. THE 
REMAINDER OF THE REGION W OF 110W IS DOMINATED BY A MID TO UPPER 
HIGH CENTERED NEAR 22N120W. THIS HIGH IS RESPONSIBLE FOR 
PROVIDING THE NE/ELY SHEAR OVER THE TROPICAL WAVE ALONG 116W. 
BESIDES FOR THE MOISTURE PLUME ACROSS THE TROPICAL BELT S OF 
19N...PRODUCED MOSTLY BY THE TROPICAL WAVES AND THE ITCZ...DRY 
STABLE AIR DOMINATES THE REMAINDER OF THE REGION W OF 110W 
ENHANCED BY A SOMEWHAT CONFLUENT PATTERN.

THE FLOW ACROSS THE TROPICAL EPAC E OF 110W IS PRIMARILY ELY 
THOUGH IT IS PERTURBED BY AN UPPER LOW LOCATED OVER SW MEXICO 
NEAR 20N98W. BESIDES FOR THE SPECIAL FEATURE...THERE IS NOT MUCH 
MORE THAN ISOLATED SHOWERS IN THIS AREA.

$$
CANGIALOSI