000 AXPZ20 KNHC 091815 AAA TWDEP Tropical Weather Discussion...Updated NWS National Hurricane Center Miami FL 1815 UTC Sat Dec 09 2017 Updated Special Features Section 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 1200 UTC surface analysis and satellite imagery through 1745 UTC. ...SPECIAL FEATURES...Updated Gulf of Tehuantepec Storm Warning: An Ascat pass from 1536Z this morning showed an area 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. Model guidance indicates that these winds will continue to intensify throughout the course of the day as very strong high pressure center of 1035 mb located over N central 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 already having cleared the Gulf of Mexico region, and is now over the western Caribbean followed by the tight packing of isobars associated with the strong high pressure over Mexico. 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 86W-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. The gale force winds will be more confined to within 30 nm of the coast of northern Costa Rica beginning Sunday afternoon and through Monday. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The Monsoon Trough axis extends from 09N79W to 09N93W to 08N104W to low pres near 09N115W 1010 mb to 10N121W to low pres near 11.5N125W 1011 mb to 10N135W, where latest scatterometer data indicated the ITCZ begins and continues SW to beyond 09N140W. Scattered moderate isolated strong convection is within 60 nm S of the axis between 122W-126W. Scattered moderate convection is within 60 nm S of the axis between 79W-81W, 107W-110W, and between 111W-116W. Similar activity is within 30 nm of the axis between 96W-98W and also w of 130W. ...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 event. High pressure N of the area is supporting a tight pressure gradient over Baja California and NW Mexico. Strong winds are present from 23N to 25N E of 114W to the coast of Baja California. Global models suggest the winds will subside to 20 kt or less today, mainly S of 28N with maximum seas to 8 ft. Winds will remain 20-25 kt north of 30N tonight, then diminish on Sunday. N-NE winds funneling through the Baja California peninsula into the Pacific waters will diminish this morning, 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. 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. 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. N-NE 25-30 kt winds are expected within 30 nm of the coast of EL Salvador early on Sunday, then diminish to 20-25 kt in the afternoon and continue through early on Monday before diminishing further to 10-15 kt Monday afternoon. 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 32N121W to 22N111W to 16N116W to 08N124W to 02N140W. The long period NW swell will mix with shorter period NE swell originating from gap wind effects in Baja California this morning. 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 to the W of a line from 32N135W to 27N140W along with waveheights in the range of 8-12 ft in NW swell. This front will reach from near 32N137W to 27N140W early Sunday afternoon preceded by strong S to SW winds within 120 nm to its E, and followed by strong NW winds and seas in the 12-16 ft in a NW swell. This front will also begin to weaken as it reaches from near 32N135W to 26N140W by late Sunday night, with winds both ahead of it and behind it diminishing to 15-20 kt. The main impact at that time will be the lingering 12-16 ft seas in NW swell behind it, and seas of 8-11 ft within 180 nm to its SE. 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. $$ Aguirre