000 AXPZ20 KNHC 102205 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Fri Nov 10 2017 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. ...SPECIAL FEATURES... ...A GALE WARNING IS IN EFFECT FOR THE GULF OF TEHUANTEPEC... A Gale Warning is in effect for the Gulf of Tehuantepec. The 1800 UTC surface analysis depict a tight pressure gradient across southeastern Mexico. This suggests that a gap flow wind event is occurring as a cooler air mass in the wake of Gulf of Mexico frontal boundary surges southward along the eastern slopes of the Sierra Madre mountains. In this case, the tightness of the gradient is indicative the surge of this air mass is translating as strong to gale force N-NE winds pushing southward out across the Gulf of Tehuantepec where sea surface temperatures are quite warm. Latest model guidance suggests that the synoptic pattern set up will remain quite favorable for gap flow of gale force northerly winds to continue through the next few days. The guidance indicates that the present N-NE 25-35 kt winds will increase further to 35-40 kt beginning on Sunday night and through early next week. Seas are in the 10-14 ft range with the current gale force winds, but given the expected long duration and intensity of these winds these seas are forecast to build to a maximum of 17 or 18 ft on Tuesday. The leading edge of 8 ft seas that will propagate SSW away from the Gulf is forecast to reach near 08N100W on Tuesday. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from southern Costa Rica to 08N93W to 10N107W to 08N116W to low pressure near 10N129W 1010 mb to 09N140W. Scattered moderate isolated strong convection is within 60 nm N of the axis between 109W-118W. Scattered moderate convection is within 60 nm S of the axis between 83W-87W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the special features section for information about the ongoing Gulf of Tehuantepec Gale Warning. A ridge will dominate the waters W of Baja California during the next several days, while a trough will meander along the coast of NW Mexico and into the Gulf of California. Moderate NW flow will prevail across the waters W of Baja California from today until early Monday. The surface pressure gradient W of Baja California will begin to significantly tighten on Sunday night and through early next week as high pressure to the W of the area builds eastward towards northern Baja California. As a result, expect fresh to locally strong NW winds to the N of about 25N and E of 119W to the coast of Baja California from early Monday to early Tuesday, with seas building to around 9 ft. Long period NW swell producing seas to the range of 8-10 feet will continue to propagate southeastward across the waters N of 23N to the W of Baja California through tonight while subsiding, and reach southward to the waters W of the southern portion of the peninsula on Sunday as it subsides further to 7-8 ft. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Light variable winds, and seas of 4-6 ft, are expected N of 09N, while moderate to locally fresh southerly winds and seas of 5-7 ft are forecast S of 09N through early next week. REMAINDER OF THE AREA... Long period NW swell that followed in behind a former frontal system that recently dissipated over the northern waters is confined to NW and N of a line from 30N116W to 20N121W to 12N127W to 14N140W, with induced seas of 8-10 ft. This swell is beginning to mix with a southerly swell component. The NW swell will propagate southeastward and southward through Saturday night reaching to an area defined from 08N-20N between 114W-131W and from 12N-20N W of 131W by Sunday afternoon and from near 12N-20N W of 124W by Monday afternoon. Global model guidance as well the medium range guidance coordinated between WPC and NHC points to a late season tropical low pressure system expected to develop along the monsoon trough near 12N133W by early Sunday afternoon or possibly sooner. The guidance indicates the pressure gradient between the low and high pressure ridging that exists over the area will pinch off into a swath of NE-E winds within about 120 nm of the low in its northern semicircle on Sunday with associated seas of 9-11 ft. The low is not expected to develop into a tropical cyclone through Sunday as the upper level winds will remain unfavorable. For now, the low once it forms, is expected to track in a general west to northwestward direction through Monday. A weak surface trough is analyzed near 137W from 11N-18N moving westward about 15 kt. The trough lies underneath the eastern periphery of a large upper level trough that is just W of the area near 141W. Upper level divergence E of the upper trough is helping to sustain scattered showers and isolated thunderstorms within 120 nm either side of the surface trough. Upper level debris cloudiness from this activity is being advected northeastward towards northern Baja California and southern California along a strong jetstream branch that rides along the eastern portion of the upper trough. The surface trough will move W of the area on Saturday as the upper trough slowly moves eastward. $$ Aguirre