000 AXPZ20 KNHC 290238 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 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 0000 UTC surface analysis and satellite imagery through 0200 UTC. ...SPECIAL FEATURES... Tropical Storm Ulika is centered near 15.8N 138.9W 1001 mb at 0300 UTC moving N or 360 DEG at 6 kt. Maximum sustained winds have diminished to 45 kt with gusts to 55 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, with the system now under a shear regime. Scattered strong convection is seen within 45 nm of the center in the north quadrant. Scattered moderate to isolated strong convection is within 90 nm of the center in the northeast quadrant. The upper trough will continue to weaken Ulika during the next 48 hours as it turns northward, then eventually decouples from the middle level circulation, leaving the low level remnant circulation to turn westward within the next 48 hours or shortly afterwards 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 22.1N 115.1W 1007 mb at 0300 UTC moving N or 360 DEG at 5 kt, or about 304 nm west- southwest of the southern tip of the Baja California Peninsula. Maximum sustained winds are 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 of the system, with convection of the scattered moderate type intensity within 30 nm of 23N115W. Roslyn is forecast to continue to weaken further to a post-tropical remnant low near 22.8N 115.4W by early on Thursday as it turns to the north and then to the northwest. It will dissipate by Friday evening well offshore of the Baja California peninsula. 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. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from Colombia near 10N74W to 10N85W to 10N94w to 13N100W...where it fractures. It then resumes from near 13N108W to 09N110W to 14N131W. Scattered moderate to isolated strong convection is noted to the southwest of the first trough segment within 30 nm of a line from 09N102W to 10N108W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... 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. A surface trough was defined on Ascat data from this afternoon, and visible satellite imagery shows that this feature is part of a broad area of organizing low pressure west of central Mexico. Deep convection within this area has diminished during the evening, however scattered moderate to isolated strong convection is observed within 60 nm of the trough. Strong upper-level west to southwest winds are blowing off the cold tops of the convection, with the residual upper moisture reaching beyond 250 nm. Global models depict the trough to continue moving westward over the next 48 hours. Any development of this trough is expected to be slow during this time period as upper level winds will be only marginally favorable. A fetch of fresh to strong east to southeast winds with seas of 6-8 ft between the trough and the coast of Mexico is expected to diminish Thursday morning as the broad area of low pressure and trough pull further away from Mexico. 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. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... 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. REMAINDER OF THE AREA... As tropical storm Ulika moves west of 140W Thursday evening 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. $$ AGUIRRE