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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 211515

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.


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.


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.



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.


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 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.