000
AXPZ20 KNHC 072202
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
2205 UTC TUE JUL 07 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 
1945 UTC.

...SPECIAL FEATURE...
TROPICAL STORM BLANCA CENTERED NEAR 19.7N 116.5W AT 2100 UTC OR 
OR ABOUT 480 NM...770 KM...WEST-SOUTHWEST OF THE SOUTHERN TIP OF 
BAJA CALIFORNIA MOVING NW OR 305 DEG AT 10 KT. MAXIMUM SUSTAINED 
WIND SPEED IS 35 KT WITH GUSTS TO 45 KT. MINIMUM PRESSURE IS 
1002 MB. SEE LATEST NHC FORECAST/ADVISORY UNDER AWIPS/WMO 
HEADERS MIATCMEP3/WTPZ33 KNHC FOR MORE DETAILS. BLANCA IS 
GRADUALLY WEAKENING WITH PULSATING DEEP CONVECTION NEAR THE 
CENTER. HOWEVER...THE BANDING STRUCTURE REMAINS WELL DEFINED. 
BLANCA IS FORECAST TO MOVE OVER COOLER WATERS OVER THE NEXT 24 
HOURS WITH THE FORECAST CALLING FOR THE STORM TO WEAKEN TO A 
REMNANT LOW OVERNIGHT WED NIGHT.

...TROPICAL WAVES...
TROPICAL WAVE WITH AN AXIS ALONG 99W FROM 05N TO 16N IS MOVING W 
AT 20 KT. THIS WAVE IS EMBEDDED IN THE ITCZ. THERE IS SCATTERED 
MODERATE WITH ISOLATED STRONG CONVECTION WITHIN 270 NM W OF 
TROPICAL WAVE FROM 10N TO 13N AS WELL AS W OF THE WAVE WITHIN 
120 NM S OF THE ITCZ AXIS BETWEEN 101W AND 107W.

TROPICAL WAVE WITH AN AXIS ALONG 84W N OF 05N IS MOVING W AT 20 
KT. THIS WAVE IS CURRENTLY PASSING THROUGH COSTA RICA...EASTERN 
NICARAGUA...AND THE NW CARIBBEAN. THIS WAVE IS EMBEDDED IN THE 
ITCZ WITH SCATTERED MODERATE CONVECTION TO THE E OF THE WAVE 
PRIMARILY E OF 83W WITHIN 150 NM S OF THE ITCZ AXIS AND N TO THE 
COAST OF PANAMA.

...ITCZ...
THE ITCZ AXIS IS ALONG 06N77W TO 10N98W TO 07N108W TO 10N117W TO 
08N140W. SCATTERED MODERATE CONVECTION CAN BE FOUND E OF 83W 
WITHIN 150 NM S OF THE ITCZ AXIS AND N TO THE COAST OF PANAMA AS 
NOTED ABOVE. SCATTERED MODERATE WITH ISOLATED STRONG CONVECTION 
LIES WITHIN 120 NM S OF AXIS BETWEEN 101W AND 107W...ALSO NOTED 
ABOVE. SCATTERED MODERATE CONVECTION CAN BE FOUND WITHIN 150 NM 
N OF AXIS W OF 138W. 

...DISCUSSION...
AN UPPER-LEVEL ANTICYCLONIC CIRCULATION IS CENTERED OVER NW 
MEXICO NEAR 29N112W WITH A RIDGE AXIS EXTENDING W ALONG 29N TO 
130W AND THEN SW TO 15N140W AND A RIDGE AXIS EXTENDING SE FROM 
THE ANTICYCLONIC CENTER TO BROWNSVILLE TX AND E ACROSS THE GULF 
OF MEXICO ALONG 25N/26N. THE UPPER PATTERN IS HIGHLY AMPLIFIED 
OVER THE FORECAST AREA TO THE S OF THIS RIDGE AXIS...WITH UPPER 
LOWS CENTERED NEAR 19N130W AND 17N103W. BETWEEN THESE LOWS LIES 
T.S. BLANCA UNDER A REGION OF WEAK UPPER LEVEL DIFFLUENCE. THE 
UPPER RIDGE AXIS TO THE N OF BLANCA IS EXPECTED TO BREAKDOWN AS 
A TROUGH MOVES INTO NW WATERS...FORCING THE UPPER LOW FROM 
19N130W NORTHWARD ALONG 130W ON ITS LEADING EDGE AND TURNING THE 
MID TO UPPER LEVEL STEERING FLOW SOUTHERLY IN THE VICINITY OF 
BLANCA. AT THE SURFACE...THE RIDGE OVER NW WATERS WILL WEAKEN IN 
RESPONSE TO THE INCREASED TROUGHING ALOFT...SENDING T.S. BLANCA 
NW AS IT GRADUALLY WEAKENS TO A REMNANT LOW OVER THE NEXT FEW 
DAYS.

SURFACE RIDGE EXTENDS FROM 30N133N TO 25N120W. BROKEN TO 
OVERCAST STRATOCUMULUS CLOUDS BLANKET THE AREA N OF 15N W OF 
122W AND APPROACHING THE SW QUADRANT OF BLANCA. THE PRESSURE 
GRADIENT BETWEEN THIS RIDGE AND THE SURFACE TROUGH ALONG 141W 
FROM 06N TO 12N IS RESULTING IN AN AREA OF NE-E TRADES OF 20 TO 
25 KT FROM 12N TO 17N W OF 137W AS SEEN IN THE 1530 UTC QUIKSCAT 
AND 1822 UTC ASCAT PASSES. THESE TRADE WINDS ARE FORECAST TO 
GRADUALLY DIMINISH IN AREAL COVERAGE DURING THE NEXT FEW DAYS. 
SCATTERED MODERATE CONVECTION CAN BE CURRENTLY FOUND E OF THE 
SURFACE TROUGH WITHIN 150 NM N OF THE ITCZ AXIS W OF 138W.

THE TROPICAL WAVE ALONG 99W FROM 05N TO 16N LIES UNDER A REGION 
OF UPPER LEVEL DIFFLUENCE TO THE S OF THE UPPER LOW NEAR 
17N103W. THE LOW LEVEL MOISTURE CONVERGENCE NEAR THIS WAVE 
COUPLED WITH THIS DIFFLUENCE ALOFT IS SUPPORTING A LARGE AREA OF 
CONVECTION TO THE W OF THE WAVE AXIS. THE UPPER LEVEL LOW IS 
EXPECTED TO CONTINUE TRACKING W WITH THE WAVE TOMORROW...BUT 
WILL BE OVERTAKEN BY THE INCREASED MID TO UPPER LEVEL TROUGHING 
TO ITS NW ON THU. STRONG EASTERLY FLOW ALOFT BETWEEN THIS LOW 
AND THE ANTICYCLONE OVER NW MEXICO IS INHIBITING DEEP CONVECTION 
OVER SOUTHERN MEXICO.

CROSS-EQUATORIAL SOUTHWEST SWELL WITH PERIODS IN THE 13-15 
SECOND RANGE CAN BE FOUND OVER MUCH OF THE N EASTERN PACIFIC E 
OF 118W. THIS SW SWELL EVENT IS EXPECTED TO CONTINUE ALONG THE 
ENTIRE COASTLINE OF THE FORECAST AREA FOR THE NEXT FEW 
DAYS...WITH SIGNIFICANT WAVE HEIGHTS GRADUALLY DECREASING OVER 
THAT TIME PERIOD.

$$
SCHAUER CLARK