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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 210918

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 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 0600 UTC surface analysis and satellite imagery through 
0900 UTC.


Tropical Storm Greg is centered near 14.5N 118.3W, or 700 nm SW 
of the southern tip of the Baja Peninsula at 2 am PDT, moving W 
at 8 kt. Estimated minimum central pressure is 1003 mb. Maximum 
sustained winds are 45 kt with gusts to 55 kt. Scattered 
moderate to strong convection is noted within 150 nm N and 100 S 
of the center. Greg is forecast to slowly intensify and reach 
hurricane strength in about 48 hours. See the latest NHC 
forecast/advisory under AWIPS/WMO headers MIATCMEP2 WTPZ22 for 
more details.

A 1009 mb surface low is along a tropical wave near 08N91W with 
scattered moderate isolated strong convection observed within 
210 nm of the W semicircle of the low. Environmental conditions 
are favorable for this low to strengthen into a tropical cyclone 
reaching near 10N94W early Sat and near 12N107W early Sun.

A 1008 mb surface low continues near 12N108W in association with 
a tropical wave. Scattered strong convection is noted within 120 
nm W of the low. The pressure gradient is supporting strong 
winds within 240 nm NE of the low. Environmental conditions are 
favorable for tropical cyclone formation as this low continues 
NW to near 14N111W early Sat and near 15N113.5W early Sun.


The monsoon trough extends from the coast of Colombia at 08N78W 
to the coast of Costa Rica at 10N85W, through a surface low at 
08N91W to 13N99W to another surface low at 12N108W to 13N112W. 
Except noted with the lows discussed above, minimal convection 
is associated with the trough axis.



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. 

Fresh to strong northerly gap winds will once again pulse to 
around 20 kt during mainly overnight and early morning hours in 
the Gulf of Tehuantepec, with a shorter pulse of strong gap 
winds again tonight into Saturday. Seas will build to 8 ft with 
an additional component of longer period southwest swell.


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.


Tropical Storm Fernanda is W of 140W, however, strong cyclonic 
winds continue from 19N-22N west OF 138W, with seas to 12 ft. 
Moderate convection is west of 140W. Fresh cyclonic winds and 7-
10 ft seas are observed elsewhere W of 136W between 14N-25N. 
Expect all associated conditions to shift W of 140W by tonight.

The remnant low of TD 8-E is analyzed near 13N126W and estimated 
pressure of 1010 MB, with strong winds continuing within 120 nm 
of the center. The low will gradually dissipate through tonight.

The pressure gradient between Fernanda and Greg 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.