000
AXPZ20 KNHC 201511
TWDEP 

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
945 UTC Thu Jul 20 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 Fernanda is centered near 18.2N 139.2W at 20/1500 
UTC moving WNW at 10 kt. Estimated minimum central pressure is 
995 mb. Maximum sustained winds are 55 kt with gusts to 65 kt. 
Scattered moderate to strong convection within 120 nm NE 
quadrant of center. Fernanda will continue to weaken as it moves 
west of 140W later today. Large swell will continue to expand 
and spread out ahead of Fernanda to the NW and W during the next 
few days. See latest NHC forecast/advisory under AWIPS/WMO 
headers MIATCMEP1/WTPZ21 for more details.

Tropical Storm Greg is centered near 14.1N 115.4, or 585 nm SSW 
of the southern tip of the Baja Peninsula at 20/1500 UTC, moving 
W at 9 kt. Estimated minimum central pressure is 1003 mb. 
Maximum sustained winds have increased to 45 kt with gusts to 55 
kt. Scattered moderate to strong convection is noted within 90 
nm of the center, except in the NW quadrant. Greg is forecast to 
slowly intensify and reach hurricane strength within 48 hours. 
See the latest NHC forecast/advisory under AWIPS/WMO headers 
MIATCMEP2/WTPZ22 for more details.

Tropical Depression Eight-E is centered near 13.4N 123.1W, or 
about 890 nm SW of the southern tip of the Baja Peninsula at 
20/1500 UTC, moving WSW at 5 kt. Estimated minimum central 
pressure is 1009 mb. Maximum sustained winds remain 25 kt with 
gusts to 35 kt. Eight-E is now experiencing southwesterly shear 
and is not expected to reach tropical storm strength. See the 
latest NHC forecast/advisory under AWIPS/WMO headers 
MIATCMEP3/WTPZ23 for more details.

A tropical wave is analyzed from 06N to 19N along 104W. A 
surface low is embedded in the wave near 12N104W with an 
estimated pressure of 1010 mb. An overnight scatterometer 
satellite pass indicated fresh to strong winds within 180 nm to 
240 nm of the center in the northeast quadrant. The low pressure 
may become a tropical cyclone as continues to the WNW with the 
wave at 10 to 15 kt over the next couple of days. Scattered 
moderate isolated strong convection observed from 07N to 12N 
between 104W and 110W, mainly along the monsoon trough. 
An additional area of scattered moderate to strong convection 
was noted within 120 nm of the coast of Mexico between 100W and 
106W. 

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

The monsoon trough extends from 08N78W to low pressure 1010 mb 
near 08N86W to the developing low pressure 1010 mb near 11N104W, 
where the monsoon trough loses definition near T.S. Greg. The 
intertropical convergence zone is west of the area. Other than 
convection already discussed above, scattered to moderate 
convection is noted within 120 nm either side of the monsoon 
trough between 87W and 94W.

...DISCUSSION...

OFFSHORE WATERS WITHIN 250 NM OF MEXICO...

Please see the special features for information on Tropical 
Storm Greg southwest of Manzanillo, Mexico. 

The weak trough west of the the Baja California peninsula has 
dissipated and has allowed the subtropical ridge to advance to 
the east. However, gentle to moderate NW winds off the Baja 
California peninsula are expected to continue through Fri. 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. 

Fresh to strong northerly gap winds will once again pulse to 
around 20 kt during mainly overnight and early morning hours
through early Friday, with a shorter pulse of strong gap winds
again Friday night into Saturday. 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...

Please see the special features section for information on 
T.S. Fernanda and Tropical Depression Eight-E.

The pressure gradient between Fernanda, and eventually the 
approaching Greg, will maintaining moderate to fresh northeast 
winds north of 25N, with seas 5 to 8 ft including components of 
northerly swell mixing with southerly swell emerging from 
Fernanda. Looking ahead, northerly swell to 8 ft will propagate 
south of 32N and west of 120W.

$$
Cobb