Eastern North Pacific Tropical Weather Discussion (Text)

AXPZ20 KNHC 290236

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0405 UTC Sat Apr 29 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 0000 UTC surface analysis and satellite imagery through
0215 UTC.


A surface trough axis extends from 10N87W to 06N94W to 06N101W 
to 04N110W, where the ITCZ axis forms and continues west- 
southwest to 02N120W to 02N130W to 01N140W. Scattered moderate/
isolated strong convection is within 60 nm of the trough axis 
between 90W and 95W and also between 97W and 103W. Scattered 
moderate convection is within 120 nm south of the trough axis
between 95W and 97W.



Strong to near gale force northwest winds continue across the 
discussion waters from 28N to 30N and west of the Baja Peninsula 
to near 125W, with seas of 9 to 13 ft in northwest swell. These 
winds and seas will persist through Saturday as a strong pressure
gradient remains over the area between high pressure to the 
west, and low pressure over the southwestern United States. Seas 
of 8 to 10 ft in northwest swell will propagate as far south as 
20N between 114W and 130W on Saturday before conditions begin to 
slowly improve over these waters Saturday night into Sunday. 

Gulf of California: Mostly gentle to moderate southwesterly flow 
is expected through tonight, with brief fresh to locally strong 
northerly winds possible over the gulf waters north of 30N 
briefly this afternoon and evening, and then Sat as a cold front 
passes across the area. The fresh to strong NW winds with and 
behind this front will shift southward into the central portions
Sat through Sat night and gradually build seas 5 to 8 ft. Winds 
and seas will decrease early on Sunday.

Gulf of Tehuantepec: Gentle to moderate south to southwest flow 
expected this weekend with fresh to strong north winds possible 
near daybreak on Monday as the gradient tightens over southeastern
Mexico as high pressure builds over the western Gulf of Mexico 
in the wake of cold front. Seas will be in the range of 3 to 5 ft
through Saturday night, then build to 5 to 7 ft Sunday through


Mostly a gentle onshore breeze is expected during the next few 
days becoming offshore along the coasts at night. Combined seas 
of 4 to 5 ft in mainly southwest swell will continue through 
these waters through tonight. Wave model guidance forecasts 
large long-period southern hemispheric southwest swell of 6 to 8
ft to approach the offshore waters of Ecuador on Saturday 
through Sunday, then subside slightly before increasing again to 
6 to 8 ft early next week.


A nearly stationary 1030 mb high pressure system well north of 
the area near 37N135W has a ridge extending southeastward to 
26N127W and to near 19N120W. This high pressure system covers the
area north of the ITCZ and west of about 115W. A tight pressure 
gradient between the high and a thermal trough along the coast of
California will continue to support strong northwest winds along
with seas of 10 to 13 ft north of 28N east of 125W through 
Saturday, before they begin subside through the remainder of the 
weekend as the gradient slackens. Fresh northeast trades are 
expected between the ridge and the ITCZ W of 125W over the next 
several days, with seas of 6 to 8 ft in mixed northeast and 
northwest swell expected through Saturday afternoon. Southern 
hemispheric swell will continue to propagate across the waters 
south of a line from the equator at 128W to 08N123W to 03N113W to
03.4S97W through Saturday, and south of 05N between 109W and 
125W on Sunday, resulting in combined seas in the general range 
of 8 to 10 ft. These seas will subside to 8 ft on Sunday.

Weak low-level westward moving perturbations continue across
the tropical belt under mid/upper level ridging. The combination
of this and a series of disturbances aloft riding along a
relatively pronounced jet stream branch is allowing for clusters
of scattered showers and thunderstorms to develop from time to 
time across this area. Latest satellite imagery shows that the 
most concentration of this activity is confined to the eastern 
portion of the tropics between 90W and 103W as described above 
under the ITCZ/Monsoon Trough section. Upper level diffluent 
flow is occurring over this portion of the area as noted in upper
level streamline analysis as well as in the trajectory of high 
level clouds within this area. This activity is likely to persist
into the weekend, with the activity west of 103W, that although 
is has diminished during the past few hours in diurnal minimum 
cycle, is expected to pulse back up late tonight or Saturday 
morning. It should then continue to pulse through Sunday.


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Page last modified: Saturday, 29-Apr-2017 02:36:54 UTC