000 AXPZ20 KNHC 052143 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2143 UTC Tue Dec 5 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 2045 UTC. ...SPECIAL FEATURES... Gulf of California: Strong high pressure is currently building from the U.S. Great Basin and northern Rockies southward towards the desert SW of the U.S., and supports near gale to gale force NW winds in the far northern Gulf N of 30N. Fresh to strong NW winds extend as far S as 28N. The gale-force winds are expected to diminish below gale this evening as the pressure gradient relaxes somewhat. Meanwhile, the fresh to strong winds will continue to expand southward across the entire Gulf through Wed night. Another area of strong high pressure will build across the region Wed night through Thu and is expected to initiate another round of gales across north and north-central portions Thu. Seas are expected to build up to 9 ft across the northern part of the basin today and to 6 to 9 ft across the remainder of the basin Wed through Thu. Also, as the strong winds develop across the Gulf, strong northeasterly gap winds will bleed through gaps in the mountain peaks across the northern peninsula and spill across the Bay of San Sebastian. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from 09N81W to 07N92W. The ITCZ extends from 07N92W to 08N110W to 10N120W to beyond 10N140W. Scattered moderate and isolated strong convection are from 08N to 17N between 121W and 130W. Isolated moderate convection is elsewhere within 90 nm of the ITCZ axis. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: Overnight drainage effects will allow winds to pulse to 20 to 25 kt tonight. Winds will increase to fresh to strong late Wed through Thu night ahead of a cold front moving across the western Gulf of Mexico, arriving in southern Mexico Thu. Winds will further increase to gale force on Fri afternoon as the cold and dry air pushes into the Gulf of Tehuantepec. Seas will build to 15 ft by early Sat, with seas 8 ft or greater reaching as far as 500 nm downstream to the W-SW of the Gulf of Tehuantepec. Looking ahead, strong high pressure building behind the front across central Mexico will support a persistent strong gale over Tehuantepec through the weekend. Elsewhere off the Pacific coast of Mexico, weak high pressure is maintaining gentle to moderate breezes across the region. High pressure building north of area will result in strong gap winds pushing across low lying areas of Baja California Norte and into adjacent waters Thu. A larger plume of strong NE winds will push off the coast of Baja California Sur north of Cabo San Lazaro Thu night and Fri, with seas 8 to 10 ft reaching from near shore to beyond 250 nm offshore. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Moderate to fresh NE winds across the Papagayo region will persist with seas downstream maintaining a range of 6 to 8 ft. Winds and seas will diminish Thu as strong trades winds across the SW Caribbean Sea diminish and veer SE. Looking ahead, strong high pressure will build N of the region, allowing strong gap winds and building seas to reappear late Sat night into Sun. Winds may even approach minimal gale force Mon. Elsewhere, light to gentle N to NE winds are expected N of the monsoon trough, and mainly gentle to moderate S to SW winds are expected to the S of the monsoon trough. Seas are in the 5 to 7 ft range in SW swell this evening to the S of the monsoon trough, and will subside to 4 to 6 ft through mid week. Large NW swell of 8 to 10 ft from the upcoming Tehuantepec gap wind event will spread across the offshore waters of Guatemala late this week and over the weekend. REMAINDER OF THE AREA... A 1011 mb complex surface low is centered near 28N138W, with an occluded front extending from near 28N139W to 28N135W, then transitioning to a stationary front to near 21N136W. The pressure gradient between high pressure N of the front and the lower pressures associated with the front will continue to support fresh to strong SE to S winds N of the front through late tonight. The low and associated front will dissipate by Wed morning. However at the same time, an approaching front W of the area will support the development of strong southerly winds N of 26N and W of 133W and NW swell of 8 to 12 ft N of 21N and W of 132W through Wed night. The front W of the area will then weaken Thu and dissipate just NW of the discussion area early Fri as winds diminish over the area. Although winds will diminish, NW swell greater than 8 ft will continue to affect these waters through the end of the week. Looking ahead, strong southerly flow will return Sat N of 28N W of 135W ahead of yet another cold front approaching from the NW. Elsewhere, long period swell to 9 ft persisting across much of the area south of 20N will decay below 8 ft through Fri. A new round of NW swell to 9 ft will propagate into the discussion area, encompassing the region N of 15N W of 130W by Thu night, then most of the area W of 120W by late Fri into Sat, mixing with shorter period NE waves N of 20N and E of 125W. $$ Latto