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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 212115

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 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 1800 UTC surface analysis and satellite imagery through 
2115 UTC.


Tropical Storm Greg is centered near 14.9N 120.7W, or 780 nm SW 
of the southern tip of the Baja Peninsula at 21/2100 UTC, moving 
WNW at 11 kt. Estimated minimum central pressure is 1003 mb. 
Maximum sustained winds have decreased to 45 kt with gusts to 55 
kt. Visible satellite imagery shows the well defined low level 
center becoming completely exposed this afternoon with 
convection displaced from the center. Scattered moderate to 
strong convection is noted within 120 nm in the NE quadrant of 
the center. Greg is forecast to begin slowly intensifying on Sat 
with peak intensity expected to remain below hurricane strength 
on Sun. See the latest NHC forecast/advisory under AWIPS/WMO 
headers MIATCMEP2 WTPZ22 for more details.

Tropical Depression Nine-E is centered near 9.0N 94.7W, or about 
420 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 banding features within 120 in the NW 
and 60 nm in the SE semicircles of the center. An additional 
area of strong convection was noted from 11.5N to 13N between 
95W and 97W. Environmental conditions are favorable for 
additional strengthening and the system could become a tropical 
storm later overnight. See the latest NHC forecast/advisory 
under AWIPS/WMO headers MIATCMEP4 WTPZ24 for more details.

A 1008 mb surface low continues near 14N110W in association with 
a tropical wave along 110W/111W. Scattered moderate to strong 
convection is confined to within 180 nm in the W semicircle of 
the low due to the presence of persistent northeasterly shear. 
Environmental conditions are favorable for tropical cyclone 
formation as this low continues NW to near 15N113W Sat and near 
16N116W by Sun.


The monsoon trough extends from the coast of Colombia at 08N78W 
to the coast of Costa Rica at 10N85W to 09N91W. The monsoon 
trough breaks down in the vicinity of newly formed T.D. Nine-E 
and a surface low near 14N110W, then resumes from 14N120W to the 
remnant low of T.D. Eight-E near 12N127W to 12N131W. The ITCZ 
extends from 12N131W to 10N140W. Scattered moderate convection 
was noted within 120 nm in the S quadrant of the low near 12N 



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 northerly gap winds of 20-25 kt are expected to pulse 
through the Gulf of Tehuantepec overnight into Sat morning 
toward developing T.D. Nine-E. 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.

REMAINDER OF THE AREA... The remnant low of TD 8-E is analyzed 
near 12N128W and estimated pressure of 1011 MB, with fresh to 
strong winds continuing within 120 nm of the center. The low 
will gradually dissipate through Sat. 

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.