000
AXPZ20 KNHC 041603
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
1605 UTC SAT MAY 04 2013

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. THE FOLLOWING INFORMATION IS 
BASED ON SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND 
METEOROLOGICAL ANALYSIS.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
1515 UTC.

...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...

MONSOON TROUGH AXIS EXTENDS FROM 06N76W TO 08N79W TO 06N85W TO  
09N103W WHERE IT TERMINATES. THE ITCZ EXTENDS FROM 08N114W TO 
BEYOND 05N140W. SCATTERED MODERATE TO STRONG CONVECTION NOTED 
WITHIN 150 NM S OF TROUGH FROM 91W TO 101W. ISOLATED TO 
SCATTERED MODERATE TO STRONG CONVECTION NOTED WITHIN 90 NM S OF 
ITCZ FROM 117W TO 129W.

...DISCUSSION... 

AN UPPER LEVEL BLOCKING PATTERN CONTINUES TO DOMINATE THE 
HEMISPHERE THIS MORNING...AND IS FORECAST TO PERSIST FOR THE 
NEXT FEW DAYS. A WELL DEFINED MIDDLE TO UPPER LEVEL CYCLONE AT 
28N137W AND HAS BEGUN TO SHIFT SLOWLY E...WITH ASSOCIATED TROUGH 
EXTENDING S TO 20N138W. FLAT UPPER LEVEL RIDING DOMINATES THE 
DEEP TROPICS...WITH STRONG S TO SW FLOW DOMINATING BETWEEN THE 
THESE TWO FEATURES...AND BROAD CONVERGENCE YIELDING A GENERALLY 
DRY STABLE AND SUBSIDENT PATTERN N OF 20N. BROAD UPPER RIDGING 
CONTINUES OVER THE MONSOON TROUGH AND ITCZ E OF 125W...AND IS 
BEING MAINTAINED BY DEEP CONVECTIVE GROWTH BETWEEN 90W AND 120W. 
THE CYCLONE IS FORECAST TO CONTINUE MOVING E-NE OVER THE WEEKEND 
AND ENTER SOUTHERN CALIFORNIA AND BAJA CALIFORNIA NORTE SUNDAY 
EVENING...AND LEAVE NEARLY ZONAL FLOW ALOFT N OF 20N BY MONDAY.

...AT THE LOWER LEVELS...

THE NE PACIFIC HIGH PRES RIDGE REMAINS WELL REMOVED FROM THE 
AREA...CENTERED ON A 1032 MB HIGH NEAR 48N136W WITH RIDGE 
EXTENDING S INTO THE NW CORNER OF THE DISCUSSION AREA. A BROAD 
AND WEAK LOW LEVEL TROUGH IS PRESENT UNDERNEATH THE UPPER 
CYCLONE AT 28N137W...AND BLOCKS THE SURFACE RIDGE FROM EXTENDING 
INTO THE AREA. LIGHT TO MODERATE NE TRADE WINDS LESS THAN 20 KT  
WERE DEPICTED BY OVERNIGHT SCATTEROMETER PASSES N OF THE ITCZ 
AND W OF 120W. 
 
LOW TO MIDDLE LEVEL CONVERGENCE NEAR THE ITCZ IS ACTING TO 
ACCUMULATE TROPICAL MOISTURE NEAR THE ITCZ BETWEEN 100W AND 
114W...PRODUCING A VERY UNSTABLE ENVIRONMENT WHERE ACTIVE 
CONVECTION DESCRIBED ABOVE PREVAILS. THIS AREA OF CONVECTION IS 
EXPECTED TO SHIFT VERY SLIGHTLY WWD DURING THE NEXT 24 HOURS. 

GULF OF TEHUANTEPEC...AN OVERNIGHT ASCAT PASS AT 0405 UTC 
SAMPLED THE REGION AND CONFIRMED 35-40 KT GALE FORCE WINDS. 
HOWEVER...NORTHERLY WINDS THROUGH THE BAY OF CAMPECHE AND INTO 
THE CHIVELA PASS ARE WEAKENING...AND GLOBAL MODELS SHOWED GALE 
FORCE WINDS ENDING AROUND 1200 UTC ACROSS TEHUANTEPEC. WINDS AND 
SEAS WILL DIMINISH THROUGHOUT THE DAY...WITH WINDS BELOW 20 KT 
AND SEAS BELOW 8 FT ACROSS THE GULF OF TEHUANTEPEC BY EARLY 
TONIGHT. 
 
SOUTH TO SOUTHEAST WINDS ARE EXPECTED TO INCREASE THIS AFTERNOON 
INSIDE THE GULF OF CALIFORNIA...AS ELONGATED LOW PRES EXTENDING 
FROM SOUTHERN CALIFORNIA ACROSS THE BAJA CALIFORNIA DEEPENS 
SLIGHTLY WITH THE HEATING OF THE DAY. WINDS WILL INCREASE TO 15-
20 KT INSIDE THE GULF OF CALIFORNIA THIS AFTERNOON THROUGH THIS 
EVENING...WITH SEAS BUILDING 3 TO 5 FT...AND THEN DIMINISH 
OVERNIGHT. NO SIGNIFICANT CHANGES TO THIS OVERALL TRANQUIL 
WEATHER PATTERN ACROSS THE REGION ARE EXPECTED DURING THE NEXT 
FEW DAYS.

$$
STRIPLING