000
AXPZ20 KNHC 211019
TWDEP 

TROPICAL WEATHER DISCUSSION 
NWS NATIONAL HURRICANE CENTER MIAMI FL                         
1005 UTC THU MAY 21 2015

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 
0900 UTC.
 
...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH...  
         
THE ITCZ AXIS EXTENDS FROM 03N89W TO 10N115W. THE MONSOON TROUGH 
EXTENDS FROM 09N115W TO 06N119W TO LOW PRES NEAR 08.5N131W 1010 
MB TO LOW PRES NEAR 08N137.5W 1009 MB TO BEYOND 04N140W. 
SCATTERED MODERATE TO STRONG CONVECTION NOTED FROM 01.5N TO 08N 
E OF 83.5W. SCATTERED MODERATE TO STRONG CONVECTION NOTED N OF 
15N TO MEXICAN COAST BETWEEN 97W AND 103W. ISOLATED TO SCATTERED 
MODERATE ISOLATED STRONG CONVECTION NOTED WITHIN 180 NM N AND 
120 NM S OF ITCZ BETWEEN 89W AND 115W. SCATTERED TO LOCALLY 
NUMEROUS MODERATE TO STRONG CONVECTION NOTED WITHIN 210 NM N AND 
270 NM S OF MONSOON TROUGH BETWEEN 115W AND 139W. 

...DISCUSSION...                                           

N OF 15N E OF 120W...A PAIR OF UPPER LEVEL IMPULSES UPPER 
IMPULSES ARE PIVOTING EASTWARD THROUGH THE BASE OF A SHARP UPPER 
TROUGH EXTENDING FROM OFF NORTHERN CALIFORNIA TO ROUGHLY 30N122W 
TO 24N123W. THESE IMPULSES WILL MOVE INTO SOUTHERN CALIFORNIA 
AND THE NORTHERN COAST OF BAJA CALIFORNIA NORTE LATER TODAY. 
THIS PATTERN HAS BEEN REINFORCING LOW PRESSURE CENTERED OVER 
SOUTHERN CALIFORNIA AS WELL AS KEEPING HIGH PRESSURE WEST OF THE 
AREA NEAR 28N123W FAIRLY WEAK. EXPECT A MODEST OF 20 TO 25 KT SW 
WINDS OVER THE FAR NORTHERN GULF OF CALIFORNIA THIS MORNING 
THROUGH ABOUT MIDDAY FRIDAY IN RESPONSE TO THE LOW PRESSURE IN 
THE AREA...WITH WINDS THEN DIMINISHING FRI AS THE UPPER SUPPORT 
LIFTS NE AND THE LOW PRESSURE WEAKENS. MEANWHILE SHIP 
OBSERVATIONS AND OVERNIGHT SCATTEROMETER SATELLITE DATA 
INDICATED ONLY MODERATE NORTHWESTERLY WIND FLOW ALONG THE COAST 
OF BAJA CALIFORNIA DUE TO THE WEAKENED HIGH PRESSURE W OF THE 
AREA. SEAS THERE WERE RUNNING 4-6 FT. LOOKING AHEAD...DEEP LAYER 
RIDGING WEST OF THE AREA WILL BUILD IN THE WAKE OF THE EXITING 
UPPER TROUGH...ALLOWING THE SURFACE HIGH PRESSURE TO BUILD 
SE...PRODUCE A SLIGHT INCREASE IN NORTHWESTERLY WINDS ALONG THE 
BAJA COAST. AFTERNOON WINDS WILL INCREASE TO AROUND 20 KT OVER 
THE WEEKEND...WITH SEAS BUILDING TO 5 TO 7 FT.

ELSEWHERE...THE TROUGHING PREVAILING ACROSS N PORTIONS HAS BEEN 
HELPING TO MAINTAIN A WEAK SURFACE HIGH PRES CENTER ACROSS NE 
PORTIONS...CURRENTLY 1019 MB NEAR 27N123W. A STRONGER RIDGE WILL 
BUILD NORTH OF THE AREA THROUGH FRI BEHIND THE EXITING UPPER 
TROUGH. A SERIES OF EASTERLY WAVES MOVING WESTWARD ACROSS THE 
DEEP TROPICS ACROSS CENTRAL AND WEST PORTIONS OF THE AREA HAVE 
CONTINUED TO INDUCE VERY ACTIVE CONVECTION THERE. LOW PRESSURE 
ACROSS THIS REGION HAS EVOLVED INTO A MONSOON THROUGH SEGMENT 
EXTENDING FROM 09N115W TO 06N119W TO LOW PRES NEAR 08.5N131W 
1010 MB TO LOW PRES NEAR 08N137.5W 1009 MB TO BEYOND 04N140W. 
THE PRESSURE GRADIENT BETWEEN THE WEAK HIGH TO THE N AND THIS 
TROUGH WILL MAINTAIN 15 TO 20 KT NE TRADE WINDS SOUTH OF THE 
RIDGE...AND CONTINUE TO INDUCE CLUSTERS OF SHOWERS AND 
THUNDERSTORMS N OF THE TROUGH. LOOKING AHEAD TO SAT AND 
SUN...GLOBAL MODELS INDICATE SOME SLOW AND MODEST DEVELOPMENT OF 
THESE LOW PRESSURE CENTERS OVER THE FOLLOWING SEVERAL 
DAYS...WITH INCREASED TRADEWIND FLOW TO AROUND 20 KT AND SEAS 
BUILDING TO 9 FT.

S OF 15N E OF 110W...AN UPPER LEVEL CYCLONIC CIRCULATION THAT 
WAS NEAR 06N97W YESTERDAY HAS SHIFTED SOUTH OF THE GALAPAGOS 
OVERNIGHT...WITH A BROAD CYCLONIC CIRCULATION CONTINUING HERE S 
OF 15N. THIS CIRCULATION CONTINUES TO ENHANCE CONVECTION ALONG 
THE ITCZ SOUTH OF 08N AND EAST OF 97W. THIS SHARP UPPER 
TROUGHING CENTERED ALONG 93W WILL WEAKEN AND BE REPLACED BY 
UPPER RIDGING ORIENTED E-W ALONG 10N BY LATE FRI. AREAS OF 
SHOWERS AND THUNDERSTORMS WILL PERSIST HOWEVER ESPECIALLY ALONG 
THE CENTRAL AMERICAN COAST DURING THE MORNINGS...AND CLOSER TO 
100W WHERE DIVERGENCE ALOFT ON THE WESTERN PERIPHERY OF AN  
UPPER RIDGE WILL ENHANCE CONVECTION. LOW LEVEL FLOW WILL REMAIN 
WEAK AND DISORGANIZED IN THE DEEP TROPICS EAST OF 120W...EXCEPT 
FOR PULSES OF 15 TO 20 KT GAP WINDS INTO THE GULF OF PAPAGAYO 
DURING THE OVERNIGHT HOURS. LOOKING AHEAD...GLOBAL MODELS HINT 
OF BROAD BUT WEAK LOW PRESSURE AREAS FORMING ALONG 08N-10N 
BETWEEN 90W AND 110W BY EARLY NEXT WEEK. 

LONG PERIOD SOUTHERLY SWELL PRODUCING WAVE HEIGHTS TO 9 FT AND 
PERIODS OF 16 TO 18 SECONDS WILL MOVE ACROSS THE EQUATOR TODAY 
THROUGH FRI...DECAYING TO BELOW 8 FT BY LATE FRI BUT DELIVERING 
4 TO 6 FT OF SWELL TO THE COASTLINES OF CENTRAL AMERICA AND 
SOUTHERN MEXICO LATE FRI AND SAT. THESE LONG PERIOD SWELLS WILL 
GENERATE LARGE AND DANGEROUS SURF CONDITIONS ALONG THESE 
COASTLINES THROUGH THE UPCOMING WEEKEND.
 
$$
STRIPLING