000
AXPZ20 KNHC 071603
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC THU MAY 07 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 
1415 UTC.

...ITCZ...
AXIS WAS ALONG 07N77W TO 09N85W TO 06N93W TO 08N112W TO 05N140W. 
SCATTERED MODERATE CONVECTION WAS WITHIN 150 NM S AND 60 NM N OF 
AXIS BETWEEN 81W AND 92W. SCATTERED TO NUMEROUS WITH ISOLATED 
STRONG CONVECTION WAS WITHIN 180 NM OF AXIS BETWEEN 104W AND 
140W.  

...DISCUSSION...
WELL ESTABLISHED REX BLOCK PATTERN ACROSS EPAC BETWEEN 145W AND 
95W HAS INDUCED A SPLIT UPPER FLOW PATTERN...WITH BROAD UPPER 
WLYS ACROSS CENTRAL PACIFIC AT 155W DIVERTED NE AND SE AROUND 
THE UPSTREAM BLOCK. 

WEAKENING MID TO UPPER LEVEL CYCLONIC CIRCULATION WAS CENTERED 
NEAR 25N138W...AND CONTINUED TO GRADUALLY LIFT N AND FILL. TWO 
S/W'S IN THE SRN STREAM FLOW OF EQUATORIAL WLYS WERE MOVING 
E...AND UNDERNEATH THIS LIFTING LOW...ALONG 142W AND 136W...AND 
WILL COME INTO PHASE NEXT 24-36 HOURS. AMPLE MID TO UPPER 
MOISTURE REMAINS AHEAD OF THE S/W ALONG 136W...BUT NO BROAD 
SCALE LIFT...AND NOW WEATHER WAS OCCURRING IN THIS MOIST REGION. 
THE UPSTREAM BLOCKING HIGH-LOW COUPLET WERE LOCATED NEAR 28N113W 
AND 17N111W RESPECTIVELY. AN ELONGATED DEFORMATION ZONE WAS 
EVIDENT IN WATER VAPOR IMAGERY SEVERAL DEGREES TO THE W AND SW 
OF THESE FEATURES...AND WAS MAINTAINING SINKING MOTION AND 
STABLE CONDITIONS. THE LOW IN THIS COUPLET IS FORECAST BY THE 
GFS TO SLIDE SLOWLY NW AND CUT OFF FROM THE CONNECTING UPPER 
TROUGH EXTENDING ENE ACROSS CENTRAL MEXICO. THIS LOW IS EXPECTED 
TO GRADUALLY WEAKEN AND FILL OVER THE WEEKEND...AND THEN LIFT N 
AND EJECT OUT TO THE NE THROUGH THE FIRST PART OF NEXT WEEK. 

THE SRN STREAM UPPER WLYS REMAIN ACTIVE AND WILL CONTINUE SO 
THROUGH THIS PATTERN CHANGE NEXT WEEK...AND WILL CONTINUE TO 
FAVORABLY INTERACT WITH THE ITCZ MOISTURE AND ENHANCE CONVECTION 
THERE E OF 140W. VERY ACTIVE CONVECTION WAS OCCURRING ON EITHER 
SIDE OF THE ITCZ THIS MORNING BETWEEN 120W AND 108W...WITH 
SCATTERED CLOUD TOPS TO -65C AND COLDER. N OF THE ITCZ...A LOW 
LEVEL CONVERGENCE LINE HAS DEVELOPED FROM JUST SE OF THE GULF OF 
TEHUANTEPEC...SW TO THE ITCZ ALONG 112W...WITH ABUNDANT MOISTURE 
CLEARLY EVIDENT IN PW IMAGES S OF THIS BOUNDARY. ISOLATED 
CONVECTION WILL REMAIN ACTIVE ALONG AND SE OF THIS MOISTURE 
DISCONTINUITY OVER THE NEXT FEW DAYS. FURTHER E...UPPER RIDGING 
ACROSS COLOMBIA...THE EXTREME TROPICAL EPAC AND SRN CENTRAL 
AMERICA CONTINUED TO VENTILATE CLUSTERS OF DEEP CONVECTION ALONG 
THE ITCZ THERE...UNDER DIFFLUENT ANTICYCLONIC FLOW ALOFT.

AT THE SURFACE...A 1028 MB HIGH WAS CENTERED NEAR 35N136W AND 
BRIDGED OVER A STATIONARY FRONTAL BOUNDARY N OF THE AREA AND TO 
ITS SE. A RIDGE EXTENDED SE TO NEAR 16N110W. THE THERMAL TROUGH 
ACROSS THE BAJA AND GULF OF CALIFORNIA HAS DISSIPATED...LEAVING 
A WEAKENED GRADIENT ALONG THE BAJA COAST...WITH FRESH NW TO N 
WINDS NOW CONFINED FARTHER N AND W FROM RECENT DAYS. PULSES OF 
NW SWELL WILL CONTINUE TO MOVE INTO THE REGION TO MAINTAIN SEA 
HEIGHTS TO AROUND 12 FT ACROSS NE PORTIONS. ADDITIONALLY...VERY 
LONG PERIOD SRN HEMI SWELL FROM THE SSW HAS REACHED THE PACIFIC 
COASTS OF CENTRAL AMERICA...AND WILL PRODUCE MODERATE TO 
OCCASIONALLY LARGE SURF ALONG THE COASTS THERE THROUGH MEXICO 
DURING THE NEXT 48 HOURS.

$$
STRIPLING