566  
AXPZ20 KNHC 211515  
TWDEP  
 
TROPICAL WEATHER DISCUSSION  
NWS NATIONAL HURRICANE CENTER MIAMI FL  
1605 UTC FRI JUL 21 2017  
 
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.  
   
..SPECIAL FEATURES
 
 
 
TROPICAL STORM GREG IS CENTERED NEAR 15.1N 119.2W, OR 700 NM SW  
OF THE SOUTHERN TIP OF THE BAJA PENINSULA AT 21/1500 UTC, MOVING  
WNW AT 9 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1001 MB.  
MAXIMUM SUSTAINED WINDS ARE NOW 50 KT WITH GUSTS TO 60 KT.  
SCATTERED MODERATE TO STRONG CONVECTION IS NOTED WITHIN 90 NM IN  
THE NW AND 45 NM IN THE SE SEMICIRCLES OF THE CENTER. GREG IS  
FORECAST TO SLOWLY INTENSIFY AND REACH HURRICANE STRENGTH IN 36  
TO 48 HOURS. SEE THE LATEST NHC FORECAST/ADVISORY UNDER  
AWIPS/WMO HEADERS MIATCMEP2 WTPZ22 FOR MORE DETAILS.  
 
NEWLY FORMED TROPICAL DEPRESSION NINE-E IS CENTERED NEAR 9.0N  
93.5W, OR ABOUT 440 NM SSE OF PUERTO ANGEL, MEXICO, MOVING W AT  
12 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 1008 MB. MAXIMUM  
SUSTAINED WINDS ARE 30 KT WITH GUSTS TO 40 KT. SCATTERED  
MODERATE TO STRONG CONVECTION WAS OBSERVED IN A LARGE BANDING  
FEATURE WITHIN 120 TO 150 NM IN THE SE SEMICIRCLE AND 180 NM IN  
THE W QUADRANT OF THE DEPRESSION. ENVIRONMENTAL CONDITIONS ARE  
FAVORABLE FOR ADDITIONAL STRENGTHENING AND THE SYSTEM COULD  
BECOME A TROPICAL STORM LATER TODAY. SEE THE LATEST NHC  
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMEP4 WTPZ24 FOR  
MORE DETAILS.  
 
A 1008 MB SURFACE LOW CONTINUES NEAR 13N109W IN ASSOCIATION WITH  
A TROPICAL WAVE ALONG 109W/110W. SCATTERED STRONG CONVECTION IS  
CONFINED TO WITHIN 180 NM IN THE SW QUADRANT OF THE LOW DUE TO  
THE PRESENCE OF NORTHEASTERLY SHEAR. THE PRESSURE GRADIENT IS  
SUPPORTING STRONG WINDS WITHIN 240 NM OF THE LOW. ENVIRONMENTAL  
CONDITIONS ARE FAVORABLE FOR TROPICAL CYCLONE FORMATION AS THIS  
LOW CONTINUES NW TO NEAR 14N112W EARLY SAT AND NEAR 15N114W  
EARLY SUN.  
   
..INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH
 
 
 
THE MONSOON TROUGH EXTENDS FROM THE COAST OF COLOMBIA AT 08N78W  
TO THE COAST OF COSTA RICA AT 09N85W, TO THE VICINITY OF NEWLY  
FORMED T.D. NINE-E NEAR 08N95W TO 12N100W TO ANOTHER SURFACE LOW  
AT 13N109W TO 14N112W, THEN RESUMES FROM 13N120W TO THE REMNANT  
LOW OF T.D. EIGHT-E NEAR 12N127W TO 12N130W. THE ITCZ EXTENDS  
FROM 12N130W TO 10N140W. EXCEPT NOTED WITH THE SYSTEMS  
DESCRIBED ABOVE, MINIMAL CONVECTION IS ASSOCIATED WITH THE  
TROUGH AXIS.  
   
..DISCUSSION
 
 
OFFSHORE WATERS WITHIN 250 NM OF MEXICO...  
 
GENTLE TO MODERATE NW WINDS OFF THE BAJA CALIFORNIA PENINSULA  
ARE EXPECTED TO CONTINUE THROUGH SAT. SEAS WILL REMAIN 5 TO 7 FT  
IN A MIX OF LONG PERIOD NORTH AND SOUTHWESTERLY SWELL. GENTLE  
SOUTHERLY FLOW WILL PERSIST IN THE GULF OF CALIFORNIA, EXCEPT  
FOR MODERATE SOUTHERLY FLOW OVER THE NORTHERN GULF.  
 
STRONG TO NEAR GALE FORCE NORTHERLY GAP WINDS PULSED THROUGH THE  
GULF OF TEHUANTEPEC THIS MORNING TOWARD DEVELOPING T.D. NINE-E.  
WINDS WILL ONCE AGAIN PULSE TONIGHT AND EARLY SAT BUT ONLY TO 20-  
25 KT. SEAS WILL BUILD TO 8 FT WITH AN ADDITIONAL COMPONENT OF  
LONGER PERIOD SOUTHWEST SWELL.  
 
OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND  
WITHIN 750 NM OF ECUADOR...  
 
IN THE GULF OF PAPAGAYO, MODERATE TO FRESH OFFSHORE WINDS WILL  
PULSE TO FRESH EACH NIGHT WITH NOCTURNAL DRAINAGE THROUGH THE  
WEEK, OCCASIONALLY BUILDING MAX SEAS TO 8 FT IN A MIX OF EAST  
SWELL AND LONGER PERIOD SOUTHWEST SWELL.  
 
GENTLE TO MODERATE SOUTHERLY WINDS ARE EXPECTED SOUTH OF THE  
MONSOON TROUGH AXIS. LONG PERIOD CROSS-EQUATORIAL SOUTHERLY  
SWELL AND 6-7 FT SEAS WILL CONTINUE TO PROPAGATE INTO THE WATERS  
REACHING THE COAST OF CENTRAL AMERICA THROUGH THE DAY. ANOTHER  
PULSE OF LARGE SOUTHERLY SWELL WILL MOVE INTO THE REGION TODAY  
AND RAISE SEAS TO 6-8 FT THROUGH TONIGHT.  
 
REMAINDER OF THE AREA...  
 
TROPICAL STORM FERNANDA HAS MOVED FURTHER W OF 140W WITH WINDS  
AND SEAS DIMINISHING TO 20-25 KT AND 8-9 FT FROM 19N-22N WEST OF  
135W. THE RESIDUAL EFFECTS OF FERNANDA WILL SHIFT W OF 140W BY  
THIS EVENING.  
 
THE REMNANT LOW OF TD 8-E IS ANALYZED NEAR 12N127W AND ESTIMATED  
PRESSURE OF 1010 MB, WITH FRESH TO STRONG WINDS CONTINUING  
WITHIN 120 NM OF THE CENTER. THE LOW WILL GRADUALLY DISSIPATE  
THROUGH TONIGHT.  
 
THE PRESSURE GRADIENT BETWEEN FERNANDA AND GREG AND HIGH  
PRESSURE TO THE N OF THE AREA WILL MAINTAIN MODERATE TO FRESH NE  
WINDS N OF 25N AND W OF 127W THROUGH THE UPCOMING WEEKEND.  
NORTHERLY SWELL IN THE FORM OF 7-8 FT SEAS WILL PROPAGATE S OF  
32N BETWEEN 125W AND 135W EARLY NEXT WEEK.  
 

 
COBB  
 
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