National Hurricane Center's Tropical Weather Discussion

Eastern Pacific Ocean

221 AXPZ20 KNHC 121559 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1332 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 1200 UTC surface analysis and satellite imagery through 1445 UTC. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from low pres 1010 mb near 08N75W to 05N79W to 07N86W to 06N93W. The ITCZ continues from 06N93W to 08N114W to 08N124W, then resumes from 09N130W to beyond 07N140W. Scattered moderate and isolated strong convection is noted within 60 nm either side of a line from 05.5N76.5W to 02.5N80.5W. A surface trough splitting the ITCZ extends from 07N130W to 11N128W to 15N125W. Divergent upper-level winds on the SE side of an upper-level low centered near 21N141W is supporting a large area of convection in the vicinity of the surface trough. Scattered moderate and isolated strong convection is found within an area bounded by 10N121W to 11N128W to 18N128W to 17N115W to 13N108W to 10N121W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec...Winds diminished below gale force this morning and are expected to rapidly decrease through this evening as high pressure over the Gulf of Mexico weakens and shifts east. Light to gentle winds are then expected through Thu night. The area of 8 ft seas generated by the latest gap wind events over the Gulfs of Tehuantepec and Papagayo involves most of the forecast waters from 01N to 16N between 86W and 110W. This area of seas has already merged with the large area of 8 ft seas associated with long period NW swell which encompasses almost all of the forecast waters W of 110W. A cold front forecast to move into the Gulf of Mexico on Thu is expected to initiate another strong gale force wind event Fri through Sun. Broad high pressure centered NW of the area near 33N140W ridges SE to near the Revillagigedo Islands. The gradient between the high and troughing over interior portions of Mexico is supporting gentle N to NW winds over the Gulf of California. Model guidance suggests that the pressure gradient will begin to tighten tonight as high pres builds over the Great Basin of the United States. Fresh to strong winds are expected accordingly over almost all of the Gulf of California Thu through Fri. 6 to 8 ft seas in NW swell across the offshore waters of Baja California will continue over the region through this morning, then subside below 8 ft by Thu morning. Another push of large NW swell will reach the waters west of Baja California Thu night. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo...A broad plume of NE winds extends across the Papagayo region to near 08N91W this morning, where seas are running between 8-10 ft. Winds will subside to between fresh and strong tonight, then diminish to moderate 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. Gulf of Fonseca...Fresh to strong NE winds will persist for a few more hours this morning, diminish significantly this afternoon, then remain light to gentle through Sat night. Gulf of Panama...Strong N winds spilling across Panama over the Gulf of Panama this morning will taper to fresh this afternoon. Seas will peak around 8 ft this morning. Winds in this area could become locally strong tonight, then will taper to moderate by Thu night. 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... NW swell associated with a dissipated front supports 8 to 10 ft seas across most of the area W of 110W. High pressure centered NW of the area near 33N140W will combine with lower pressures in the vicinity of the ITCZ and a surface trough that extends from 07N130W to 11N128W to 15N125W to support fresh to strong NE trade winds generally from 10N to 25N west of 125W through Thu, with associated seas in the 9-12 ft range. The areal coverage of winds and seas will diminish tonight through Fri as the surface trough gradually weakens and the upper-level low just to the NW becomes an open wave and lifts out to the NE. $$ CAM