000 AXPZ20 KNHC 050945 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Wed Dec 05 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 0600 UTC surface analysis and satellite imagery through 0945 UTC. ...SPECIAL FEATURE... Gulf of Tehuantepec Gale Warning: Minimal gale northerly winds will persist through early tonight and reach as far s as 14.5N95.5W with seas building to 13 ft downstream near 14.5N95.5W this morning. Winds will diminish to 20 kt or less on Fri afternoon. The next gap event will begin on Sun morning with strong gale conditions developing on Sun night and persisting through Mon night. .INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends W across the far SW caribbean along 09.5N to the Pacific coast of Costa Rica at 09N84W to 09N106W to 09N107W where a N to S trough has developed from 05N110W to 13N109W. The monsoon trough resumes at 09N112W to 09N132W where scatterometer winds indicate a transition to an ITCZ which continues W to beyond 09N140W. Scattered moderate isolated strong convection is observed within 180 nm either side of a line from 04N77W to 08N88W, within 30 nm either side of a line from 06N98W to 07N104W, within 30 nm either side of a line from 05N108W to 13N107W, within 120 nm either side of a line from 09N116W to 10N127W and from 06N to 11N between 134W and 140W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec...See special features paragraph above. Gulf of California: Moderate northerly winds currently observed across the entire gulf waters will gradually diminish to a light and variable breeze throughout by late this morning. Fresh to locally strong southwesterly flow is then forecast along 31N this evening, ahead of a pre-frontal trough that will pass E through the northern gulf waters tonight and Thu, followed by the associated cold front late Thu night into Fri, with fresh northerly flow forecast briefly behind both the trough and the front. Gentle to locally moderate northerly flow expected across the entire gulf waters on Sat. Then the pressure gradient will tighten with fresh to locally strong NW flow expected across the southern and central gulf waters on Sat night and Sun. Elsewhere: Light and variable flow W of 100W except fresh southerly flow has already developed W of Baja Norte ahead of a cold front arriving at 32N120W this afternoon, and reaching the extreme northern Baja Peninsula early Thu, with the parent weak surface low passing E across the discussion waters N of 30N on Thu. Long-period NW swell, in the form of 7 to 9 ft seas, will reach 32N116.5W on Thu night, with these seas propagating S reaching the W shore of the southern Baja Peninsula late Fri night, just as they begin to subside from the N, with these seas forecast less than 8 ft by Sun evening. The next round of long-period NW swell, in the form of 7 to 9 ft seas, will reach 32N120W on Mon and propagate S across the waters W of the entire Baja Peninsula on Tue. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Thin volcanic ash originating interior Guatemala is observed on satellite imagery spreading southwest across the Pacific coast of Guatemala and Mexico between 14N and 15N, but may not be sinking to near the surface. Gulf of Papagayo...Nocturnal pulses of fresh to locally strong NE winds, and 6 to 8 ft seas, are expected through Fri night and will extends as far W as 09.5N91W on Thu. Elsewhere: The monsoon trough will meander between 08N and 10N this week with light to gentle variable flow, and 3 to 5 ft seas, forecast N of the monsoon trough, and moderate southwesterly monsoonal flow, and 4 to 6 ft seas, forecast S of the monsoon trough. REMAINDER OF THE AREA... A weak surface trough may be forming along 110W from 08N to 11N. The GFS model indicates that an inverted surface to low-level trough may form near 100W later in the week and propagate westward. A surface low will shift SE into the area to near 32N125W tonight, and then move E along 32N passing E of 120W on Thu night, while dragging a couple of cold fronts E across the subtropical waters. Large 8 to 13 ft seas, primarily due to long-period NW swell, is forecast to propagate E across the area, with the leading edge of 8 ft or greater seas reaching from 32N120W to 10N140W on Thu, and from the southern tip of the Baja Peninsula to the equator at 130W on Fri night. Another cold front will reach 32N137W on Fri accompanied by a moderate wind shift. A stronger cold front will reach 32N140W on Sat evening accompanied by a fresh wind shift and large post- frontal NW swell. $$ Nelson