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Eastern North Pacific Tropical Weather Discussion

AXPZ20 KNHC 280245

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
0405 UTC Wed Sep 28 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 0000 UTC surface analysis and satellite imagery through
0215 UTC.


Tropical Storm Roslyn is centered at 19.5 115.9W at 28/0300Z, or
about 391 nm west-southwest of the southern tip of the Baja
California Peninsula, moving northeast or 040 degrees at 8 kt. The
estimated minimum central pressure is 1004 mb. Maximum sustained
winds have diminished to 35 kt with gusts to 45 kt. Latest
satellite imagery shows that Roslyn remains a sheared tropical
cyclone with the low- level center removed well to the south of
the remaining convection due to moderate to southwesterly winds
aloft. The imagery shows the remaining plume of scattered moderate
convection between 90 nm and 210 nm of the center in the north
quadrant. Roslyn is forecast to weaken to a tropical depression
late tonight into Wednesday morning, then to a post- tropical
remnant low by early Wed afternoon...then begin to track to the
northwest later on Wednesday afternoon and through Thursday while
dissipating. Refer to the latest NHC forecast/advisory under
AWIPS/WMO headers WTPZ23 KNHC/TCMEP3, or visit the NHC website at for additional details.

Tropical Storm Ulika is located in the far western edge of the 
discussion area and high seas forecast area near 13.3N 139.1W at
28/0300Z, or about 995 nm east-southeast of Hilo Hawaii, moving
northeast or 045 degrees at 6 kt. The estimated minimum central
pressure is 997 mb. Maximum sustained winds have increased to 55
kt with gusts to 60 kt. Latest satellite imagery shows that Ulika
is becoming better during evening with tightly coiled banding
features around a small central dense overcast (CDO) feature.
Scattered strong convection is within 30 nm of the center.
Scattered moderate isolated strong convection is within 90 nm of
the center in the southeast quadrant. Scattered moderate within 90
nm of the center in the northeast quadrant. Refer to the latest
NHC forecast/advisory under AWIPS/WMO headers WTPZ24KNHC/TCMEP4,
or visit the NHC website at for additional


The monsoon trough axis extends from northwest Panama at 10N84W
to 10N90W to 12N97W to 12.5N104W to low pressure near 12N107W
1008 mb to 08N115W. It resumes at 13N117W to 12N125W to 14N129W
to 14N135W. Scattered moderate isolated strong convection is
observed within 180 nm south of the axis between 80W and 85W, 
within 60 nm of the axis between 127W and 129W and between 132W
and 134W.



A northwest to southeast oriented surface trough is analyzed from
11N96W to near Acapulco Mexico. Scattered moderate to isolated
strong convection is noted from 09N to 16N between 98W and 103W.

Relatively weak high pressure covers the area to the north 
of the tropical cyclones Rosyln and Ulika. The associated gradient
is producing light to gentle N to NE winds to the west of the
Baja Peninsula, with the exception of waters near and around the 
Rosyln. Pockets of diminishing showers and thunderstorms and
strong E winds and combined seas of 8 to 11 ft will expand
northeastward across the waters generally from 18N to 23N W of
114.5W through Wednesday night as Tropical Storm Roslyn continues
northward while weakening. The subtropical ridge will extend from
29N120W to 20N106W on Fri with gentle N flow returning. The
pressure gradient will tighten Fri. Moderate to fresh NW winds and
5 to 8 ft seas will prevail W of Baja Sat and Sun.

Light to gentle NW winds are expected across the entire Gulf of
California through Thu. Light and variable winds expected on Fri
across the far northern gulf waters.

Strong drainage flow will pulse across the Gulf of Tehuantepec
late Thursday night into Friday morning.


Light to gentle S winds expected N of the monsoon trough, while
gentle to locally moderate S to SW flow is expected to the south
of of the monsoon trough through the upcoming weekend. Combined
seas of 3 to 6 ft primarily in long-period SW swell are expected
this week.


As Ulika pulls off to the west of 140W Thursday night and Roslyn 
degrades to a remnant low, the subtropical ridge will strengthen
slightly. This will tighten the gradient over the northwest
portion of the area with northeast to east moderate winds with
seas of 6 to 7 ft expected there at that time. Gentle to moderate
NE winds with seas of 5 to 6 ft are expected elsewhere north of
the monsoon trough not affected by Roslyn or Ulika. Moderate to
occasionally fresh southerly flow and 6 to 7 ft seas will dominate
south of the monsoon trough for at least the next couple of days.