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Eastern North Pacific Tropical Weather Discussion
000 AXPZ20 KNHC 152159 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2105 UTC Tue Jan 15 2019 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... Gulf of Tehuantepec Gale Warning: High pressure over the Gulf of Mexico continues to funnel north to northeast winds through the Chivela Pass and into the Gulf of Tehuantepec. Both Ascat and Windsat data from this afternoon depicted 30-35 kt winds across and downstream from the Gulf reaching to near 14.5N and between 94W and 96W. Strong to near gale force north to northeast winds are south of 14.5N to near 12N and between 95W and 98W. The gale force winds are forecast to continue into early Wed afternoon, at which time high pressure over the northern Gulf of Mexico will shift eastward and weaken. This was allow for the strong pressure gradient over southeastern Mexico to slacken, enabling the gale force winds to lower to just below gale force. The winds will diminish further, to strong category by late Friday. Maximum seas presently reaching 14 ft with the gale force winds will gradually subside through the end of the week. For more information, refer to the East Pacific High Seas Forecast under WMO/AWIPS headers FZNT02 KNHC/HSFEP2. In the long term, a rather powerful storm-force gap wind event is possible beginning on Sun. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... A trough extends from central Colombia to the coast at 03N79W and continues to 04N85W to 04N91W, where it briefly ends. A 1012 mb low is centered near 05N104W. Latest scatterometer data indicates that the ITCZ then resumes at 04N106W and continues to 07N122W to 07N131W and to beyond 06N140W. Scattered moderate convection is seen within 30 nm of the ITCZ between 126W and 129W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Winds west of Baja California are light and variable and will remain below strong breeze through Fri morning. A developing storm over the U.S. Great Basin will help to tighten the pressure gradient and force strong breeze NW to N winds Fri and Saturday. NW swell of 8 to 11 ft are currently impacting these waters, which will gradually weaken through Thu night. A more pronounced and extensive set of northwest swell, with resulting seas possibly peaking up to 15 ft will begin to arrive beginning early on Fri and gradually subside through Sun. Gulf of California: Gentle to moderate NW winds will persist in the Gulf through early Sat. These will become strong northwest winds Sat through Sun due to the developing storm system over the Great Basin. Wind waves could reach 8 ft on the weekend. Gulf of Tehuantepec: See discussion above for on-going Gale Warning. Substantial high cloudiness with isolated showers are being advected across the water south of Baja California and into western Mexico ahead of a mid to upper-level trough along 122W. These should gradually diminish over the next couple of days. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: An Ascat pass from this afternoon indicated strong northeast winds across the Gulf due to a moderate pressure gradient over the western Caribbean and Central America. The strongest winds and areal coverage will be greater late night and early morning hours as nocturnal drainage augments the winds. Winds are expected to briefly increase to near gale force late Thu night before diminishing back to mainly strong winds Fri. Peak seas will be in the range of 8-10 ft, except possibly up to 11 ft Thu night. These conditions will continue through Sat. Gulf of Panama: An Ascat pass from thus afternoon showed strong northeast winds over the Gulf. The strongest winds and areal coverage will be greater late night and early morning hours as nocturnal drainage augments the winds. Peak seas will reach about 8 ft. These conditions will continue through Fri before weakening on Sat and Sunday. REMAINDER OF THE AREA... An overnight scatterometer pass showed SW strong breeze conditions north of 28N between 123W and 130W. These will gradually weaken and pull northward. Late tonight renewed SW strong breeze ahead of the next cold front will reach our northwestern corner at 30N140W. The front will not progress far south into the area and W to NW winds behind the front should remain at fresh breeze or weaker conditions. The main story elsewhere is that long-period northwest swell producing seas of least 8 ft covers most of the area west of 110W. Maximum seas of 14 ft are near 30N127W. These seas will slowly subside through Thu night. An extensive set of northwest swell, bringing maximum seas up to around 19 or 20 ft over the northern waters west of 125W, is forecast by the Wave models to arrive beginning early on Thu, then gradually subside through Sat as it propagates southeastward. Farther to the southeast, a weak 1012 mb low is centered at 05N104W with scattered moderate convection within 210 nm of the low in the northeast quadrant and 180 nm of the low in the southeast quadrant. Fresh to strong east winds are noted on the northern periphery of the low. The latest altimeter passes highlighted seas to 9 ft in the area of strong winds. This feature formed at the base of a negatively tilted mid/upper trough reaching into the deep tropics. The trough will continue to move westward, reaching to near 120W by Fri. Winds and seas will diminish thereafter as the trough moves west of its upper support and weakens. In addition to the trough, the area from 04N to 15N between 95W and 110W will also see combined seas of 8 to 12 ft in a mix of long period northwest swell and shorter period northeast and east swell that will propagate out of the gap wind areas. $$ Aguirre