000 AXPZ20 KNHC 110346 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Sat Nov 11 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 0000 UTC surface analysis and satellite imagery through 0315 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 0000 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 central Costa Rica to 10N84W to 08N90W to 07N100W to low pressure near 11N112W 1008 mb to low pressure near 09N121W 1007 mb to 11N129W to 09N140W. Scattered moderate convection is within 120 nm N and S of the axis between 116W- 120W, from 10N- 14N between 129W-134W, within 60 nm S of the axis between 135W- 137W and within 60 nm S of the axis W of 138W. ...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 currently analyzed along the monsoon trough as noted above near 11N112W with a pressure of 1008 mb to expected to develop slightly as it tracks west- northwestward to near 12N119W with a pressure of 1007 mb by early Saturday evening, and to near 13N126W with a pressure of 1007 mb by early on Sunday evening. 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 120-150 nm of the low in its northern semicircle on Sunday with associated seas of 9-11 ft. The low may have a better chance for development beyond Sunday night as upper level winds become more favorable with the present vertical southwesterly diminishing. Low pressure of 1008 mb is forecast to develop near 12N133W Saturday morning, and move to near 12N134W by early Saturday evening with a pressure of 1008 mb. A tight gradient over its northern semicircle should allow for E winds of 20-25 kt to occur from 12N-15N between 131W-135W through Saturday night. The low is forecast to begin to weaken after Saturday night as it nears the far western waters. This will then weaken the strong E winds to mainly fresh winds. The seas associated with the low will then be attributed to the area of NW swell swell described above in the first paragraph. A weak surface trough is analyzed from near 20N139W to 24N138W 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 trigger off isolated showers and isolated thunderstorms within 120 nm to the E 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