000 AXPZ20 KNHC 120323 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Wed Dec 12 2018 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 0200 UTC. ...SPECIAL FEATURES... Gulf of Tehuantepec Gale Warning: Strong high pressure across the Gulf of Mexico continues to produce a tight pressure gradient over the Isthmus of Tehuantepec, leading to a large area of strong gales across the Gulf of Tehuantepec and downstream to near 13.5N96W this evening. Late morning partial scatterometer passes around 1600 UTC showed 35-40 kt winds extending downstream of the Gulf to near 13.5N96W. The large area of gales has generated high seas to around 17 ft through this evening. Gale force winds will continue through tonight, and gradually diminish Wed morning to less than 30 kt, then rapidly decrease during the afternoon and become gentle to moderate by Wed evening, as high pressure over the Gulf of Mexico weakens and shifts east. Large N to NE swell will propagate well away from the source region, with the leading edge of 8 ft seas expected to reach W to 110W and S to 02N by early Wed, and merge with a larger area of 8 ft seas approaching from the northwest. Please refer to the Eastern Pacific High Seas Forecast under AWIPS/WMO headers HSFEP2/FZPN03 KNHC for more specific marine details.22 ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 07N75W TO 05.5N79W TO 07N85W TO 05.5N92W. The ITCZ extends from 05.5N92W TO 08.5N114W TO 10.5N127W to beyond 07N140W. Scattered moderate isolated strong convection is noted from 03S to 04.5N between 76.5W and 82W. Scattered moderate to strong convection is occurring from 07N to 17.5N between 115W and 137W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec...After the ongoing gale wind event quickly tapers off on Wed, light to gentle winds are expected through Thu night. A strong cold front forecast to move into the Gulf of Mexico Thu will likely initiate another gale force wind event Fri through Sun. High pressure NW of the area has a ridge axis that extends southeast to the Revillagigedo Islands. The pressure gradient between the high and troughing in the Gulf of California is supporting gentle to moderate NW winds across the entire Gulf of California. Model guidance suggests that the pressure gradient will begin to tighten Wed night, with fresh to strong winds expected over almost all of the Gulf of California Thu through Fri. 6 to 9 ft seas in NW swell current prevailing across the offshore waters of Baja California will continue over the region through Wed morning, then subside below 8 ft through Wed evening. Additional round of large NW swell will reach the waters west of Baja California late Thu. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo...A broad and significant plume of NE winds extends across the Papagayo region to near 08.5N90W this evening, where seas are 8-10 ft. Winds will pulse to just below gale force overnight, remain fresh to strong Wed night, then diminish to 10-15 kt Thu. Fresh to strong winds will return Sat and expand in coverage through the weekend. Seas of 8-10 ft can be expected during the periods of the stronger winds. Fresh to strong NE winds across the SW Caribbean are spilling across Panama and producing fresh northerly winds across the Gulf of Panama this evening, and are expected to continue through Wed night before winds begin to diminish. Seas are expected to peak near 7 ft at times of strongest winds. Elsewhere, gentle to moderate winds will persist on either side of the monsoon trough through the remainder of the week, with seas in the 4-6 ft range. REMAINDER OF THE AREA... A weakening cold front extends from 30N115W TO 25N121W TO 23N130W. NW swell associated with the front supports seas in excess of 8 ft across most of the area west of 120W. A tighter pressure gradient building between high pressure northwest of the front and lower pressures near the ITCZ will support fresh to strong NE trade winds from 09N to 25N west of 127W through Thu, with seas in the 10-13 ft range this evening subsiding to 9- 12 ft Thu. Wave model guidance suggests a rather large area of 8 ft or greater seas will stretch from about 02N to 15N between 92W and 110W as a result of long-period northwest swell mixing with shorter period northeast swell generated from current the Gulf of Tehuantepec event, and to a lesser extent those from the Gulf of Papagayo. This area of swell will merge into a larger area of seas associated with northwest swell which will cover most of the forecast area west of 92W on Wed. A surface trough is analyzed along the ITCZ near 128W-129W. Associated winds are moderate to fresh, with seas 8-10 ft. The trough is E of a pronounced upper-level trough as seen in water vapor. The upper trough will amplify southward, but the surface trough will gradually lose its identity and continue westward over the next couple of days. $$ Stripling