000 AXPZ20 KNHC 270216 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Fri Oct 27 2017 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 2145 UTC. ...SPECIAL FEATURES... Possible Tropical Cyclone Formation: A surface low is analyzed near 10.5N88.5W and is estimated at 1007 mb. Scattered moderate isolated strong convection is observed within 270 nm over the S semicircle of the low center. This low is forecast to move northwestward through the upcoming weekend, with environmental conditions favorable for tropical cyclone formation. The forecast is for strong winds, and 8 to 13 ft seas, within 150 nm of the low center on Sat. Heavy rainfall is expected across Costa Rica, Nicaragua, Honduras, and Guatemala over the next few days. Gulf of Tehuantepec Gale Warning: Strong northerly winds currently in and downstream of the gulf waters forecast to gradually diminish to 20 kt or less early Fri. The resultant large NE swell continues to propagate S and mix with long period cross-equatorial southerly swell, as well as long-period NW swell, with a plume of seas to 11 ft currently along 06N between 94W and 102W. These seas should subside to a max of 9 ft by sunrise Fri. Strong N winds will resume in the Gulf of Tehuantepec on Fri night, and increase to minimal gale force during the mid morning on Sat, with gale conditions then persisting through Sun morning. Heavy Surf Conditions: Seas of 8 to 9 ft, with 20 to 24 second wave period, are forecast to reach the Pacific coast of the Baja Peninsula on Sat night, and reach the Pacific coast of Mexico as far S as 17N on Sun night. Refractive swell at 15 to 17 seconds will arrive across the southern Gulf of California on Sun. This powerful surf energy may produce dangerous near shore conditions including rip currents and beach erosion. INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends W from the Pacific coast of Costa Rica at 10N85W through an embedded 1007 mb surface low at 10.5N88.5W to 08N101W to 10N119W where scatterometer winds indicate that an ITCZ axis forms and continues w to 11N131W then dips Sw to beyond 10N140W. Scattered moderate isolated strong convection is observed within 210 nm either side of a line from 07N83W to 09N90W to 08N98W to 15N106W, within 120 nm either side of a line from 08N105W to 14N129W to 06N140W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Heavy Surf Conditions: please refer to the special features section above for information on heavy seas arriving this upcoming weekend. Gulf of Tehuantepec: please refer to the special features section above for information on a strong gale event. Gulf of California: Light and variable winds expected through late Fri, then a moderate NW breeze is forecast through Sat night. Light and variable winds expected on Sun becoming a moderate S breeze on Mon. A surface ridge extends E across the waters W of the Baja Penisula, with light to gentle anticyclonic winds, except becoming a moderate NW breeze within 180 nm W of the Central and Southern Baja Peninsula on Fri evening. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Possible Tropical Cyclone Formation: please refer to the special features section above for information on a tropical low near 10N88W. Otherwise, moderate southerly winds, and 4 to 6 ft seas, are expected S of 08N through the upcoming weekend. REMAINDER OF THE AREA... A broad ridge dominates the EPAC waters N of 12N W of 115W accompanied by gentle to moderate anticyclonic flow, and combined seas of 5 to 7 ft to the S of 30N, while moderate to fresh NE winds are observed N of 30N W of 128W. The pressure gradient will relax on Fri. A new batch of long-period NW swell, in the form of 8 ft seas, will arrive at 32N140W early Fri. Expect seas of 8 to 13 ft W of a line from 32N123W to 13N140W midday on Sat, before beginning to subside. $$ Nelson