Eastern North Pacific Tropical Weather Discussion (Text)

AXPZ20 KNHC 282205

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2105 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 1800 UTC surface analysis and satellite imagery through
2145 UTC.


Tropical Storm Ulika is centered near 15.1N 138.7W 1000 mb at
2100 UTC moving N or 010 DEG at 6 kt. Maximum sustained winds
have diminished to 50 kt with gusts to 60 kt. Water vapor imagery
shows a broad upper trough just to the west and northwest of Ulika
with its associated upper level southwest to west winds impinging
on the cyclone. As a result, low-level cloud lines are becoming
exposed in the western semicircle. Banding features have becomes
less defined during the afternoon. Scattered moderate to strong
convection is seen within 60 nm of the center, except within 30
nm of the center in the east and west quadrants. The upper trough
will continue to weaken Ulika during the next few days as it turns
northward, then eventually decouples from the middle level
circulation, leaving the low level remnant circulation to turn
westward within three days as it remains embedded in the trade
wind flow. Refer to the latest NHC forecast/ advisory under
AWIPS/WMO headers WTPZ24KNHC/TCMEP4, or visit the NHC website at
http://hurricanes.gov 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
http:www.prh.noaa.gov/cphc/ for additional details.

Tropical Depression Roslyn is centered near 21.6N 115.2W 1007 mb
at 2100 UTC moving N or 360 DEG at 6 kt, or about 304 nm west-
southwest of the southern tip of the Baja California Peninsula.
Maximum sustained winds have diminished to 30 kt with gusts to 40
kt. Strong southwesterly upper level winds continue to create
south to southwest over Roslyn, with the low level center
completely exposed, and convection well removed from the center
within a distance from 60 to 150 nm in the north quadrant. The 
convection is of the scattered moderate to isolated strong type 
intensity. Roslyn is forecast to continue to weaken further
during the next few days as it turns to the north and then to 
the northwest, and remains well offshore of Baja California. The
remnant circulation is expected to gradually dissipate in about
three days. Refer to the latest NHC forecast/advisory under
AWIPS/WMO headers WTPZ23 KNHC/TCMEP3, or visit the NHC website at
http://hurricanes.gov for additional details.


The monsoon trough axis extends from Colombia near 10N74W to
10N85W to 11N100W to 12N107W to 06N117W...where it fractures.
It then resumes from near 13N117W to 12N126W to 13N136W. Scattered
moderate to isolated strong convection is noted 120 nm south 
of the axis between 101W and 104W, and also within 180 nm north
and 120 nm south of the axis between 115W and 118W.



A sub-tropical ridge axis extends in a northwest to southeast
orientation across the offshore zones west of the Baja California
peninsula to near 24N126W. Light to gentle n-ne winds are
observed w of the Baja Peninsula. Fresh to strong e to se
winds,and combined seas of 7 to 11 ft will expand n across the far
offshore waters, generally from 11N to 24N west of 115W tonight,
as weakening Roslyn begins to track to the northwest late tonight,
then west-northwest on Friday. The subtropical ridge will rebuild
from 29N120W to 22N106W on Fri with gentle n flow returning,
except becoming moderate along the Baja coast during the overnight
hours. The pressure gradient will tighten this weekend, with
moderate to fresh northwest winds, and 5 to 8 ft seas west of the
Baja California peninsula on Sun, and fresh to strong northwest
winds developing Sun night.

Fresh drainage flow is expected across the Gulf of Tehuantepec
tonight, increasing to fresh to strong flow on Thu, and then
pulse during the overnight hours through the upcoming weekend.


Light to gentle southerly winds are expected n of the monsoon
trough, while gentle to locally moderate south to southwest flow
is expected s of the monsoon trough through the upcoming weekend.
Combined seas of 4 to 6 ft primarily in long-period southwest
swell is expected this week.


As tropical cyclone Ulika moves w of 140W and Roslyn dissipates,
the pressure gradient will tighten around the subtropical ridge,
with fresh anticyclonic winds expected between the monsoon
trough/ITCZ and the ridge by Mon, with combined seas of 6 to 7
ft. The gradient will then relax some by the middle of next week.


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Page last modified: Wednesday, 28-Sep-2016 22:05:48 UTC