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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 252207

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 UTC Mon Sep 25 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 
2100 UTC.


Tropical Depression Pilar has degenerated into an elongated 
trough of low pressure today, now extending from near Cabo San 
Lucas in Baja California Sur to near the W coast of mainland 
Mexico, just north of Mazatlan in southern Sinaloa. All of the 
significant convection and heavy rainfall associated with this 
system has shifted NE and inland, and currently extends from 
southern Sinaloa across the Sierra Madre Occidentales to NE 
Mexico across portions of Coahuila. Winds and seas have quickly 
subsided across the Gulf of California, and the remaining 
weather threat of this remnant system is heavy rainfall across 
the mountainous interior and slopes of Mexico. See the last NHC 
Forecast/ Advisory for Pilar under AWIPS/WMO headers 
MIATCMEP3/WTNT23 KNHC for more details.


The monsoon trough axis extends from 10N75W TO 15.5N96W TO 
13N107W TO low pressure 12.5N126.5W 1010 MB TO beyond 11N140W. 
Scattered moderate to strong convection is from 03N to 14.5N E 
of 94W, from 10N to 15.5N between 94W and 104W, and from 60 nm N 
to 150 nm S of the trough between 121W and 140W.



Wind and seas associated with the remnants of Pilar will affect 
the southern Gulf of California through Tuesday, where winds 
will remain at 10 to 20 kt and seas 4 to 6 ft.

A high pressure ridge reaches SE into the waters west of Baja 
California to near 19N116W, with the associated pressure 
gradient expected to maintain moderate NW winds along the 
Pacific coast of Baja through tonight. The ridge will weaken in 
response to low pressure passing well to the north and NW winds 
will become gentle to moderate Tuesday through Thursday night. 
Fresh SW to W monsoonal winds well offshore of the Gulf of 
Tehuantepec will generate SW wind waves in the SE waters and 
maintain seas in this area of 5 to 7 ft.


An active monsoon trough near and along the coast of Central 
America from Guatemala to Panama will remain the focus for 
active convection over the coastal waters the next few days. 
Expect moderate to SW to W winds to prevail south of the trough, 
with gentle to moderate offshore or variable winds north of the 
trough through Friday night.

Long period SE to S swell will decay and allow seas west of 
Ecuador and south of the Equator to subside from around 6 ft to 
around 5 ft during the next couple of days.


NW to N swell generated by strong winds north of the area are 
producing 6 to 7 ft seas N of 20N and W of 120W. Pulses of 
reinforcing N swell will maintain seas in the region between 6 
and 8 feet through Wed night.

Fresh to strong winds occurring around low pressure embedded in 
the monsoon trough near 12.5N126.5W are supporting a surrounding 
area of 8 to 10 ft seas in mixed swell. Fresh to strong winds 
extend farther E to near 120W there, where seas are 8-9 ft. 
Monsoonal SW winds will remain fresh to strong across this 
general area between 09N and 14N through Wed and maintain seas 8-
9 ft. 

Otherwise, high pressure centered well N of the area, and low 
pressure associated with the monsoon trough will maintain 
moderate to occasionally fresh trade winds W of 120W through 
tonight. Low pressure passing north of the area will weaken the 
high, allowing trades to decrease for the remainder of the week.