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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 291611

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1605 UTC Thu Sep 29 2016

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
1500 UTC.


Tropical Storm Ulika is centered near 16.7N 139.7W 1003 mb at
1500 UTC moving NW or 320 DEG at 6 kt. The maximum sustained
wind speed is 40 kt with gusts to 50 kt. Currently, scattered
moderate to strong convection is observed within 120 nm across
the NE semicircle. Ulika continues to experience SW wind shear
and is forecast to weaken to a tropical depression within 24
hours as it continues NW and crosses 140W and into the central
Pacific. Refer to the latest NHC forecast/ advisory under
AWIPS/WMO headers WTPZ24KNHC/TCMEP4, or visit the NHC website at for additional details. After the center
moves w of 140W, refer to the latest CPHC forecast/advisory
under AWIPS/WMO headers WTPA22 PHFO/TCMCP2, or visit the CPHC
website at for additional details.   

Post-tropical cyclone Roslyn continues to slowly weaken over
thefar offshore waters this morning, centered near 23.5N
115.5W,moving NNW at 6 kt. The upper level trough to the NW of
Roslynthe past few days has sheared the middle level circulation
awayfrom the low level center, which is entering southern
Arizonathis morning. Only low clouds are left around the center
ofRoslyn with light convection occurring within 75 nm NW of
thecenter. Maximum winds are 25 kt with gusts to 35 kt, mainly
Nthrough E of the center, where seas are to 8 ft. Roslyn is
forecast to continue to spin down as a remnant low as it moves
NW during the next 24 hours. Refer to the latest NHC
forecast/advisory under AWIPS/WMO headers WTPZ23 KNHC/TCMEP3, or
visit the NHC website at for additional


The monsoon trough extends from 1010 mb low pres over Colombia
near 09N74.5W to 12N106W to 09N120W to 1011 mb low pres near
13N133.5W, where it terminates. Isolated to scattered moderate
to strong convection is observed within 60 nm N and 210 nm S
ofthe trough between 97W and 115W. 



Post-tropical cyclone Roslyn is centered near 23.5N 115.5W,
moving NNW at 6 kt, and producing seas of 6-8 ft in mixed
swellacross the outer SW portion of zone PMZ013. To the NW of
Roslyn, a sub-tropical ridge axis extends from nw to se across
the offshore zones w of the Baja Peninsula terminating near
27N123W. Light to gentle n winds continue this morning W of the
Baja Peninsula with seas 4-5 ft in mixed NW and SW swell.
Theridge will strengthen and build SE during the next few days,
and Roslyn dissipated, and gradually produce a moderate to fresh
nw flow, with 5 to 8 ft seas across the the northern two-
thirds of the Baja Peninsula on Sun. 

Light and variable winds are expected through the weekend across
the northern Gulf of California, and light to gentle nw-n flow
is expected elsewhere. Winds will increase through mid week as
the ridge builds into the region.

A high amplitude surface trough analyzed from 12N106W to
20N107W, and is expected to continue to drift w over the next
day or so. Active convection is occurring this morning in an
inverted vee pattern, around the periphery of this trough.
Isolated to scattered moderate to strong convection is from 12N
to 20N between 101W and 113W, and scattered moderate to strong
convection extends to the north from 20N to 24.5N east of 1`09W
to the Mexican coast.

Fresh to strong drainage flow has developed across the Gulf of
Tehuantepec overnight and will continue to pulse up and
downthrough the weekend, peaking near 25-30 kt with seas of 8-10
ft late at night through sunrise. 


Light to gentle southerly winds are expected n of the monsoon
trough, while gentle to locally moderate s to SW flow is
expected s of the monsoon trough through the upcoming weekend.
Combined seas of 4 to 7 ft, primarily in long-period SW swell is
expected across the offshore waters through the upcoming weekend.


As tropical cyclone Ulika moves w of 140W this afternoon through
tonight and tropical cyclone Roslyn dissipates, the pressure
gradient will tighten around the subtropical ridge, with
moderate to fresh anticyclonic winds expected between the
monsoon trough/ITCZ and the ridge through early next week, with
combined seas of 5 to 7 ft. The gradient will then relax some by
the middle of next week.