000
AXPZ20 KNHC 180910
TWDEP 

TROPICAL WEATHER DISCUSSION      
NWS NATIONAL HURRICANE CENTER MIAMI FL
1005 UTC FRI MAY 18 2012

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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0715 UTC.

...SPECIAL FEATURES...

AT 0900 UTC...TROPICAL DEPRESSION ALETTA WAS CENTERED NEAR 13.8N 
113.8W AND MOVING NE OR 045 DEG AT 3 KT. THE ESTIMATED MINIMUM 
CENTRAL PRES WAS 1005 MB. MAXIMUM SUSTAINED WINDS WERE 30 KT 
GUSTS TO 40 KT. PLEASE REFER TO THE LATEST PUBLIC ADVISORY 
TCPEP1/WTPZ31 KNHC FOR MORE DETAILS. SCATTERED MODERATE 
CONVECTION LIES WITHIN 75 NM OF TROPICAL DEPRESSION ALETTA 
EXCEPT WITHIN 150 NM N QUADRANT WHILE SCATTERED MODERATE TO 
STRONG CONVECTION CAN BE FOUND ELSEWHERE FROM 09N TO 15N BETWEEN 
110W AND 113W. WATER VAPOR AND PRECIPITABLE WATER IMAGERY SHOW A 
SHARP DEMARCATION BETWEEN THE MOISTURE ASSOCIATED WITH THE 
CYCLONE AND DRY AIR TO ITS N AND W. ALETTA WILL GRADUALLY WEAKEN 
DURING THE NEXT 48 HOURS AS THIS DRY AIR AND SHEAR ALOFT BEGIN 
TO TAKE THEIR TOLL ON THE SYSTEM.

A BROAD AREA OF LOW PRES IS EMBEDDED WITHIN THE MONSOON TROUGH 
AND CENTERED NEAR 12N100W. CONVECTIVE ACTIVITY ASSOCIATED WITH 
THE DISTURBANCE HAS BECOME MORE ORGANIZED. SATELLITE IMAGERY 
SHOWS NUMEROUS MODERATE TO STRONG CONVECTION WITHIN 210 NM NW 
SEMICIRCLE OF THE LOW PRES SYSTEM. THIS LOW LIES UNDER AN UPPER 
RIDGE THAT STEMS FROM AN ANTICYCLONE NEAR 13N93W. THIS PATTERN 
IS EXPECTED TO CHANGE LITTLE OVER THE NEXT FEW DAYS. THE SLOW 
MOVING LOW PRES SYSTEM IS EXPECTED TO INTENSIFY IN AN 
ENVIRONMENT OF FAVORABLE UPPER LEVEL DIFFLUENCE. THERE IS A 
MEDIUM CHANCE OF THE LOW BECOMING A TROPICAL CYCLONE DURING THE 
NEXT 48 HOURS.

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

THE MONSOON TROUGH AXIS EXTENDS FROM 08N78W TO 08N86W TO 13N95W 
TO 1008 MB LOW PRES NEAR 12N100W TO 14N110W. THE ITCZ AXIS 
EXTENDS FROM 08N118W TO 05N125W TO 07N140W. ISOLATED MODERATE TO 
STRONG CONVECTION CAN BE FOUND WITHIN 45 NM EITHER SIDE OF THE 
AXIS E OF 84W. NUMEROUS MODERATE TO STRONG CONVECTION LIES NE OF 
THE AXIS WITHIN 120 NM OF THE COAST OF CENTRAL AMERICA FROM 10N 
TO 14N. IN ADDITION...SCATTERED MODERATE TO STRONG CONVECTION 
LIES S OF THE AXIS E OF 82W TO THE COAST OF COLOMBIA AND FAR 
NORTHERN ECUADOR FROM 01N TO 05N.

...DISCUSSION...

NE TRADE WINDS ARE CONFINED TO A SMALL AREA N OF THE ITCZ W OF 
134W ACCORDING TO THE 0648 UTC ASCAT PASS. THE SUBTROPICAL RIDGE 
HAS WEAKENED OVER THE PAST 24 HOURS. THE 1027 MB HIGH CURRENTLY 
NEAR 34N149W WILL CONTINUE TO WEAKEN AS IT IS PUSHED EASTWARD 
TOWARD 130W OVER THE NEXT TWO DAYS. TRADE WINDS WILL DIMINISH TO 
A GENTLE TO MODERATE BREEZE BY LATER TODAY. THE PRES GRADIENT 
WILL REMAIN STRONG ENOUGH ON THE E SIDE OF THE HIGH TO GENERATE 
20 KT N WINDS WELL OFF THE BAJA PENINSULA OVER NE WATERS TODAY 
AND TOMORROW...WITH NORTHERLY SWELL KEEPING SEAS OVER 8 FT HERE 
INTO SUN MORNING.

THE 0548 UTC OSCAT PASS SHOWED N WINDS TO JUST BELOW GALE FORCE 
IN THE GULF OF TEHUANTEPEC. WHILE THE NORTHERLY FLOW THROUGH 
ISTHMUS OF TEHUANTEPEC IS BEING FORCED BY THE PRES GRADIENT 
BETWEEN RIDGING IN THE WESTERN GULF OF MEXICO AND TROUGHING OVER 
THE E COAST OF THE YUCATAN PENINSULA...WINDS AS STRONG AS THOSE 
SEEN IN THE OSCAT PASS SEEM UNLIKELY. THE EDGE OF THE 0324 UTC 
ASCAT PASS CLIPPED THE WESTERN SIDE OF THIS GAP WIND EVENT AND 
WAS ABOUT 5-10 KT LOWER THAN THE OSCAT PASS. THE PROXIMITY TO 
LAND MAY BE ARTIFICIALLY ENHANCING THE OSCAT RETRIEVALS SINCE 
OSCAT HAS A LIMITED LAND MASK. WINDS ARE BELIEVED TO BE A FRESH 
TO STRONG BREEZE IN THE GULF OF TEHUANTEPEC THIS MORNING AND 
WILL DIMINISH BELOW A FRESH BREEZE AROUND SUNSET AS THE RIDGING 
IN THE WESTERN GULF ERODES. 

$$
SCHAUER