999 AXPZ20 KNHC 181553 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1552 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 1200 UTC surface analysis and satellite imagery through 1500 UTC. ...TROPICAL WAVES... A tropical wave is analyzed N of 05N along 85W and is estimated to be progressing W at 10 to 15 kt. Scattered moderate and isolated strong convection is noted near the tropical wave and along the monsoon trough from 04N to 08N east of 88W. A tropical wave is analyzed from 05N101W to 16N100W and is estimated to be progressing W at 15 kt. Scattered moderate convection is noted from 11N to 14N between 98W and 104W. A tropical wave is analyzed from 06N115W 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 11N127W through a 1011 mb surface low embedded along the wave at 16N127W to 20N126W. This system is moving W at 15 kt. Scattered moderate convection to isolated strong convection is noted within 90 nm in the northeast quadrant of the low pressure. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 08N78W to 08N99W. A segment of the ITCZ reaches from 08N102W to 10N113W. Another segment of the ITCZ reaches from 10N117W to 13N123W. A third segment of the ITCZ reaches from 12N120W to beyond 10N140W. In addition to the convection listed in the tropical waves section, scattered moderate convection is noted within 90 nm either side of the monsoon trough between 92W and 97W, and within 120 nm either side of the ITCZ west of 135W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Gulf of Tehuantepec: Local nocturnal drainage flow along with a somewhat tight pressure gradient between high pressure over the Gulf of Mexico and lower pressure father south are together supporting strong gap winds into the Gulf of Tehuantepec, accompanied by 6 to 8 ft seas. The winds and seas will taper off through late morning as drainage effects weaken. Strong gap winds will again pulse tonight, but will be smaller in areal extent and not persist as long as the current event with seas not reaching 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, in the form of 7 to 8 ft seas, will arrive along 03.4S to the E of 93W late today, and propagate N reaching the far offshore waters between 05N and 14N W of 86W late Sun, with this swell reaching the coast of Central America late Mon. REMAINDER OF THE AREA... A mid/upper low centered over 23N130W, supporting the weakening surface low near 16N127W, 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 93W and 133W late Sat, and reach along 18N to the E of 130W early Mon. 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