000
AXPZ20 KNHC 011554
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC THU OCT 01 2009

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

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1545 UTC.

...SPECIAL FEATURE...
THE AREA OF BROAD LOW PRES CENTERED NEAR 19N117W HAS ATTAINED 
ENOUGH ORGANIZATION TO BECOME TROPICAL DEPRESSION EIGHTEEN-E. 
THE DEPRESSION WAS CENTERED NEAR 19.0N 117.9W AT 01/1500 UTC OR 
ABOUT 525 NM...935 KM...WEST-SOUTHWEST OF THE SOUTHERN TIP OF 
BAJA CALIFORNIA WITH MAXIMUM SUSTAINED WINDS OF 30 KT WITH GUSTS 
TO 40 KT. THE DEPRESSION WAS MOVING WEST-NORTHWEST OR 285 DEG AT 
7 KT WITH AN ESTIMATED MINIMUM CENTRAL PRESSURE OF 1004 MB. 
SCATTERED TO NUMEROUS STRONG CONVECTION IN BANDS WAS NOTED 
WITHIN 120 NM OF THE CENTER OF THE DEPRESSION. ADDITIONAL 
CONVECTION WAS NOTED WELL E OF THE CENTER WITHIN45-60 NM EITHER 
SIDE OF A LINE FROM 20N113W TO 17N114W TO 13N116W. THE 
DEPRESSION COULD STRENGTHEN INTO A TROPICAL STORM OVER THE NEXT 
12 TO 24 HOURS HOWEVER THIS WINDOW OF OPPORTUNITY IS RATHER 
NARROW AS WATER VAPOR IMAGERY INDICATED MODERATE TO STRONG 
SOUTHERLY SHEAR NOT TOO FAR W OF THE TROPICAL CYCLONE. 
ADDITIONAL INFORMATION CAN BE FOUND UNDER AWIPS/WMO HEADERS 
MIATCMEP3/WTPZ23 KNHC.

...TROPICAL WAVE...
TROPICAL WAVE FROM 08N TO 16N ALONG 107W WAS MOVING W ABOUT 12 
KT OVER THE PAST 24 HOURS. ISOLATED MODERATE CONVECTION WAS 
NOTED WITHIN 90 NM OF THE WAVE AXIS FROM 12N TO 16N. 

...ITCZ...
AXIS IS ALONG 07N78W TO 11N105W TO 09N140W. SCATTERED MODERATE 
ISOLATED STRONG WITHIN 90 NM EITHER SIDE OF AXIS E OF 85W. 
SCATTERED MODERATE WITHIN 60 NM EITHER SIDE OF AXIS BETWEEN 125W 
AND 130W.

...DISCUSSION...
RATHER AMPLIFIED PATTERN IN PLACE S OF 30N WITH A SHARP SHEAR 
AXIS EXTENDING FROM SOUTHERN CALIFORNIA WESTWARD THROUGH 32N128W 
TO A CYCLONIC CIRCULATION NEAR 29N140W. A MORE SIGNIFICANT 
TROUGH CONTINUED SOUTH-SOUTHWESTWARD TO A BASE NEAR 15N145W. 
SATELLITE DERIVED WINDS INDICATED A 70-90 KT JETSTREAM SE OF THE 
TROUGH WHICH EXTENDED FROM 15N140W 23N135W TO NORTHERN BAJA 
CALIFORNIA. MODERATE TO STRONG SUBSIDENCE WITH DRY STABLE AIR IN 
THE MIDDLE AND UPPER LEVELS OF THE ATMOSPHERE WAS NOTED WITHIN 
THE SHEAR AXIS AND SWEEPING AROUND THE BACKSIDE OF TROUGH N OF 
15N W OF 140W. DOWNSTREAM UPPER LEVEL ANTICYCLONIC CIRCULATION 
IS CENTERED NEAR 22N108W...WITH RIDGE N TO THE NORTHERN COAST OF 
THE BAJA PENINSULA. UPPER LEVEL DIFFLUENT FLOW SW OF THE 
ANTICYCLONIC CIRCULATION IS ENHANCING CONVECTIVE ACTIVITY IN THE 
VICINITY OF NEWLY FORMED TROPICAL DEPRESSION EIGHTEEN-E. 

AN INVERTED TROUGH IN THE DEEP TROPICS WITH AXIS FROM THE 
EQUATOR AT 98W TO 10N90W WAS NEARLY STATIONARY. MODERATE TO 
STRONG SUBSIDENCE IS WITH THE TROUGH S OF 7N E OF 100W.

AT THE SURFACE...
STRONG RIDGE OF HIGH PRES COVERED THE AREA N OF 20N W OF 115W. 
THE RIDGE COMBINED WITH THE LOWER PRESSURES IN THE TROPICS AND 
IN THE VICINITY OF TROPICAL DEPRESSION EIGHTEEN-E HAS RESULTED 
IN A LARGE AREA OF NE TRADES OF 20 TO 25 KT GENERALLY N OF 20N
AND W OF 120W. 

$$
COBB