000 AXPZ20 KNHC 092155 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Sat Dec 9 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 2100 UTC. ...SPECIAL FEATURES...Updated Gulf of Tehuantepec Storm Warning: The most recent scatterometer pass showed an area of N-NE 35-45 kt winds roughly within 60 nm of a line from 16N95W to 14N95.5W. This area of strong gale force winds was embedded within a broad area of N-NE gale force of 30-35 kt within 120 nm of a line from 16N95W to 14N95.5W to 13N96W. Seas are quite large, in the 14-20 ft range within the area of 35-45 kt winds and 13-18 ft within the area of 30-35 kt winds. Winds are forecast to further increase tonight into early Sun morning as very strong high pressure center of 1035 mb located over N central Mexico develops a tight pressure gradient over southeastern Mexico to just N of the Isthmus of Tehuantepec. As a result, the ongoing strong gale force winds are now forecast to intensify to storm force of maximum value of 55 kt by this evening. This is sooner than was earlier anticipated. This will be an impressive blast of storm force winds given the favorable synoptic set-up that is taking shape with a strong cold front currently located over the NW Caribbean. The storm force winds are forecast to last through early on Sunday before weakening slightly to just below storm force early in the afternoon. Quite impressively, maximum waveheight with these storm winds are expected to reach the range of 15-23 ft on Sunday, and only subside slightly late on Sunday aternoon. A large area of gale force winds of 30-40 kt is forecast to be elsewhere of the storm force winds within 120 nm of a line from 16N95W to 15N95W to 13N97W, including the Gulf of Tehuantepec through Sunday. Seas to 12 ft are expected to propagate well away from the Gulf to near 04N and 106W on Sunday, and farther W to near 110W on Monday. These gale force winds are forecast to continue into early next week while gradually tapering off, however, marine impacts with respect to resultant very large seas will affect waters to the S and SW of the Tehuantepec well into next week. Gulf of Papagayo Gale Warning: Strong high pressure building N of the area as describe above with the Gulf of Tehuantepec warning will induce a strong gap wind event across the Gulf of Papagayo beginning near 03Z tonight into early Sunday morning, at which time NE winds are forecast to reach minimal gale force of 30-35 kt. N-NE winds of 20-30 kt are expected elsewhere downstream from the gale force winds over an area defined from 07N-11N between 85W-88W early on Sunday morning, and from 06N- 10N between 86W-90W early on Monday with sea heights to 9 ft in NE swell derived from the gale force winds. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The Monsoon Trough extends from 08N82W to 08N100W to low pres near 10N114W 1008 mb to 11N124W to 10N135W. The ITCZ axis continues from 10N135W to beyond 09N140W. Scattered moderate convection is from 06N to 09N between 95W and 100W. Similar convection is from 07N to 11N between 120W and 131W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: Please see Special Features section above for details on an ongoing strong gale event soon to become a storm gap wind event. High pressure over the Great Basin will continue to support fresh to strong northerly winds over the northern Gulf of California through Sunday. N-NE winds funneling through the Baja California peninsula into the Pacific waters have diminished 15-20 kt, with seas subsiding below 8 ft off the coast of Baja California through tonight. Elsewhere gentle to moderate winds and 4-6 ft seas will persist through next week. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Please, see Special Features section above for a soon to begin gale event. Large NW swell with seas of 8-10 ft from a strong Tehuantepec gap wind event mentioned above will spread across the offshore waters of Guatemala through Sunday. Localized gap wind pulses of 20-25 kt are possible south of El Salvador and Guatemala, and through Gulf of Fonseca beginning late Sunday night and diminishing to 20-25 kt during Monday morning and to 15-20 kt Monday afternoon. 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 S of the trough. Seas are 4-7 ft in SW swell S of the monsoon trough. REMAINDER OF THE AREA... Long period NW swell has spread across the forecast waters covering roughly the area to the W of a line from 30N125W to 20N112W to 04N130W to 02N140W. A cold front has just crossed into the far NW part of the area, but it is starting to weaken. This front will dissipate by early on Sunday, however, a stronger cold front will be approaching the NW corner at the same. The pressure gradient between it and high pressure over the northern is expected to develop strong S to SW winds N of 28N W of 135W along with waveheights in the range of 9-14 ft in NW swell. The front is forecast to reacg a position from 30N135W to 25N140W by Sun night while weakening. Seas of 12-14 ft in NW swell will follow the front. These conditions will continue into Monday, then gradually decay through the middle part of next week. Yet another set of NW swell is forecast by wave model guidance to approach the far NW portion by that time. $$ GR