614 AXPZ20 KNHC 182152 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2037 UTC Wed Jul 18 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 1800 UTC surface analysis and satellite imagery through 2100 UTC. ...TROPICAL WAVES... A tropical wave is analyzed N of 05N along 88W and is estimated to be progressing W at 10 to 15 kt. Scattered moderate convection is noted near the tropical wave and north the monsoon trough from 06N to 10N between 85W and 90W. A tropical wave is analyzed from 07N103W to 16N103W and is estimated to be moving W at 15 kt. Scattered moderate convection is noted from 10N to 13N between 100W and 105W. A tropical wave is analyzed from 07N120W to 17N113W and is estimated to be progressing W at 15 kt. Scattered moderate isolated strong convection is noted near the tropical wave and along the ITCZ from 06N and 13N between 114W and 121W. A tropical wave is analyzed from 11N128W through a 1012 mb surface low embedded along the wave at 17N128W to 19N128W. This system is moving W at 15 kt. Scattered moderate convection convection is noted within from 16N to 18N between 123W and 126W. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 07N78W to 10N125W. The ITCZ reaches from 11N130W to beyond 09N140W. In addition to the convection listed in the tropical waves section, scattered moderate convection to isolated strong convection is noted within 90 nm either side of the monsoon trough east of 84W, and scattered to moderate convection is noted within 90 nm either side of the ITCZ west of 135W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: High pressure north of the area in the Gulf of Mexico along lower pressure south of the region will interact with local drainage flow to produce a brief pulse of 20 to 25 kt gap winds into the Gulf of Tehuantepec overnight. The duration and extent of the stronger gap winds will keep significant wave heights below 8 ft. Gap winds will relax through the remainder of the week until late Sat into early Sun, when the potential for strong gap winds return. Elsewhere, weak ridging across the region from the north central Pacific through the Revillagigedo Islands continues to support gentle to moderate NW flow across the Mexican offshore areas, with 3 to 5 ft seas in open waters. An upper trough is migrating from over the Gulf of California through Baja California, supporting a few diminishing showers over the central Gulf of California. Seas will build to 5 to 7 ft from south to north starting Fri mainly due to long period SW swell propagating into the open offshore waters of Mexico. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Fresh to strong nocturnal easterly drainage flow, accompanied by 6 to 8 ft seas, are expected through Thu night with extended guidance suggesting these nocturnal conditions will resume on Sun night. Gentle to occasionally moderate E winds are forecast elsewhere N of the monsoon trough which is meandering between 07N and 10N. Moderate southerly winds are forecast S of the monsoon trough for the next several days accompanied by 4 to 6 ft seas. Long period southerly swell is approaching the equator this evening, and will continue to propagate northward, reaching the far offshore waters of Panama and Costa Rica late week with seas to 8 ft, the encompassing the remainder of the Central American offshore waters Sun into early next week. REMAINDER OF THE AREA... A mid/upper low centered over 24N129W, supporting the weakening surface low near 17N128W, will drift northward through the next couple of days to 29N125W. This will keep the subtropical ridge relatively weak, thus maintaining only moderate to occasionally fresh trade wind flow deeper into the tropics. Long period cross-equatorial swell, in the form of 7-9 ft seas, is moving across the equator between 90W and 125W, and will continue to propagate N reaching across the discussion area S of 10N between 90W and 135W late Sat, and reach along 18N to the E of 130W early next week. Long period northerly swell, in the form of 7-9 ft seas, will arrive along 32N between 125W and 132W late Thu night, then propagate SW across the discussion waters from 30N to 32N between 130W and 140W during the upcoming weekend and then subside on Mon. $$ Christensen