000 AXPZ20 KNHC 252157 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2157 UTC Sun Sep 25 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 2100 UTC. ...SPECIAL FEATURES... Newly formed Tropical Depression Eighteen-E is near 16.1N 119.6W at 25/2100Z or about 680 nm southwest of the southern tip of the Baja California peninsula, moving north at 5 kt. Estimated minimum central pressure is 1005 mb. Maximum sustained wind speed is 30 kt with gusts 40 kt. Numerous moderate showers and thunderstorms are active within 210 nm of the southeast semicircle of the center of T.D. Eighteen-E. The depression is forecast to intensify to tropical storm strength tonight and move within 180 nm to the west of Clarion Island Monday night before weakening. See latest NHC forecast/advisory under AWIPS/WMO headers WTPZ23 KNHC/TCMEP3 or visit the NHC website at http://hurricanes.gov for more details . ...TROPICAL WAVES... A tropical wave is located to the north of 08N along 96W/97W drifting west. This likely enhanced a large area of late night and early morning showers and thunderstorms in the Gulf of Tehuantepec that have since diminished. Another area of showers and thunderstorms has persisted over Panama and Costa Rica and their adjacent waters over the past couple of days, propagating slowly westward. Specifically, scattered moderate to isolated strong convection is noted north of 04N between 80W and 87W off western Panama and southwest Costa Rica. This may be evidence of another tropical wave moving from the southwest Caribbean into the eastern Pacific. Unlike the previous tropical wave, this tropical wave would be fairly low latitude and is probably better defined in the lower to mid levels of the atmosphere than at the surface. The main impact will be persistent scattered to numerous showers and thunderstorms over the next couple of days mainly east of 80W. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 10N86W to 11N97W to 08N107W to 09N113W. It resumes at 13N123W to 1011 mb low pressure near 11N139W to beyond 11N140W. Scattered moderate convection is within 60 nm south of the monsoon trough axis between 92W and 100W and within 120 nm south of axis between 135W and 140W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... The pressure gradient between relatively low pressure over southern Arizona and northwest Sonora compared to strong high pressure farther north over the Great Basin is contributing to the potential for fresh eastern winds across the far northern Gulf of California from late tonight through Monday, locally reaching 25 kt at times. Wave height development will be limited by fetch however, and winds will diminish by late Monday. Elsewhere winds and seas will remain fairly limited across the region through mid week, except in areas beyond 200 nm off Baja California Sur that will be impacted by increased winds and seas by mid week on the periphery of the by then weakening T.D. Eighteen-E, tracking mainly just outside of the offshore waters zones. Farther south, a cold front is forecast to move across the Gulf of Mexico waters early in the week. High pressure behind the front will likely induce the first Gulf of Tehuantepec gap wind event of the season with fairly weak pulse Tuesday night into Wednesday morning followed by a strong pulse Wednesday night into Thursday morning. At this time, marine guidance suggests northerly winds of 20-25 kt and building seas to 8 ft by early Thursday. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Mainly light and variable winds are noted north of the monsoon trough while gentle to locally moderate south to southwest flow is expected south of monsoon trough the middle of the week. Combined seas of 3-6 ft, primarily in long-period southwest swell, are expected through the middle of the week. REMAINDER OF THE AREA... An area of low pressure located near 12N138W or about 1100 nm east-southeast of the Big Island of Hawaii continues to produce disorganized showers and thunderstorms. Satellite imagery indicates scattered moderate convection within 120 nm in the southeast quadrant of the center of the low pressure. Any development of this disturbance should be slow to occur during the next couple of days. After that time, environmental conditions could become more conducive for development. This system is expected to move west-northwestward during the next couple of days, and then turn northward as it approaches the Central Pacific basin. The pressure gradient between this low and the subtropical ridge to the north is resulting in an area of fresh to strong northeast from 13N-22N W of 130W. An earlier altimeter pass provided observations of combined seas of 8 to 12 ft within the area of the trade winds. This marine conditions will diminish in areal extent, covering the waters from 13N to 17N between 135W and 140W by this evening. Seas of 8 to 9 ft will persist from 12N to 16N west of 138W through early Monday morning, just north of the low pressure. $$ CHRISTENSEN