000 AXPZ20 KNHC 181526 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1605 UTC Wed Oct 18 2023 Tropical Weather Discussion for the eastern Pacific Ocean from 03.4S to 30N, east of 120W including the Gulf of California, and from the Equator to 30N, between 120W and 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 1450 UTC. ...SPECIAL FEATURES... Tropical Storm Norma is centered near 14.8N 107.9W at 18/1500 UTC, moving north-northwest at 6 kt. Estimated minimum central pressure is 991 mb. Maximum sustained wind speed is 60 kt with gusts to 75 kt. Peak seas are currently around 22 ft. Numerous moderate scattered strong convection is noted within 420 nm in the NE quadrant, 600 nm in the SE quadrant, and 180 nm in the W semicircle. Norma is moving toward the north-northwest. A north- northwestward to northward motion at a similar forward speed is expected during the next few days. Rapid strengthening is forecast during the next day or so, and Norma is expected to become a hurricane later today. Gradual weakening is forecast by late this week. Swells generated by Norma will begin to affect portions of the coast of southwestern Mexico today. These swells will spread northward along the coast of western Mexico and toward Baja California Sur during the next couple of days. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. Please read the latest HIGH SEAS FORECAST issued by the National Hurricane Center at website - https://www.nhc.noaa.gov/text/MIAHSFEP2.shtml and the latest Norma NHC Forecast/Advisory and Public Advisory at www.hurricanes.gov for more details. Gulf of Tehuantepec Gale Warning: The area of high pressure across the eastern slopes of Mexico that was responsible for the tight pressure gradient across the area has started to shift eastward, and the pressure gradient has started to loosen. Gale- force winds are in the process of diminishing, however the pressure gradient will remain tight enough to support pulsing fresh to strong winds through the remainder of the week. Peak seas are currently around 12 ft, but are also subsiding. Please read the latest NHC High Seas Forecast at website www.hurricanes.gov/marine for more details. NW Swell in the NW waters: Large NW swell has propagated into the NW waters. Seas of 12 ft have reached 30N140W and now to near 28N136W per an earlier altimeter pass. Seas greater than 12 ft will continue propagating SE, and will cover the waters N of 25N and W of 135W by early this afternoon. Seas will peak around 15 ft this afternoon through the overnight hours near 30N140W. This swell will continue to spread SE with seas 8 ft or greater covering the majority of the waters W of 100W by the end of the week, when peak seas should subside to just below 12 ft. Confused and hazardous seas will be the result of the combination of the NW swell, SW swell moving N of the Equator, and swells generated by Tropical Storm Norma by the end of the week. Seas will gradually decay from west to east Fri night through the upcoming weekend. Please read the latest NHC High Seas Forecast at website www.hurricanes.gov/marine for more details. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 10N75W to 08N90W to 10N100W, then resumes SW of Norma near 10N117W to low pressure near 10N123W to 06N140W. Scattered moderate isolated strong convection is noted from 06N to 11N between 89W and 100W. ...OFFSHORE WATERS WITHIN 250 NM OF MEXICO... Please see the SPECIAL FEATURES section above for more details on Tropical Storm Norma, and the ongoing Gulf of Tehuantepec Gale Warning. Aside from Tropical Storm Norma and the Gulf of Tehuantepec Gale Warning, a ridge extends across the Baja California offshore waters. Gentle to moderate winds prevail west of the Baja California peninsula with light to gentle winds elsewhere offshore Mexico, including in the Gulf of California, except where a plume of fresh to strong winds from the Gulf of Tehuantepec gap wind event feeds into the outer circulation of Norma beyond the nearshore waters of SW and southern Mexico. Seas are in the 6-8 ft range offshore Baja California Norte, and 4-7 ft elsewhere over the open waters off Mexico. Seas of 1-2 ft are noted over the Gulf of California. For the forecast, Norma will strengthen to a hurricane near 15.8N 108.1W this evening, move to 16.9N 108.3W Thu morning, 17.8N 108.5W Thu evening, 18.7N 109.0W Fri morning, 19.6N 109.5W Fri evening, and 20.8N 109.9W Sat morning. Norma will change little in intensity as it moves to 21.9N 109.9W early Sun. Elsewhere, winds over the Gulf of Tehuantepec are diminishing below gale force now. Fresh to strong winds will continue to pulse over the Tehuantepec region through the remainder of the week. Seas in the Tehuantepec region will subside through the day as winds diminish. Gentle to moderate winds will prevail elsewhere through the end of the week. Fresh to strong winds offshore Baja California may develop this weekend. Large NW swell is forecast to spread offshore Baja California by the end of the week into the weekend, resulting in confused and hazardous seas as it mixes with swells generated by Norma. Looking ahead, a broad area of low pressure has formed several hundred nautical miles south of the Gulf of Tehuantepec but is only producing a few disorganized showers and thunderstorms. Gradual development of this system is expected, and a tropical depression is likely to form late this week or over the weekend while the system meanders or drifts northwestward over the far eastern portion of the basin. This system has a low chance of tropical cyclone development in the next 48 hours, and high chance through 7 days. ...OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Fresh to locally strong gap winds are over the Papagayo region, with moderate to fresh winds extending downstream of Papagayo to near 10N94W. Light to gentle winds are noted elsewhere N of the monsoon trough. Gentle to moderate winds are S of the monsoon trough. Seas are in the 5-8 ft range well offshore Guatemala, 5-7 ft over and downstream of the Gulf of Papagayo, and 3-5 ft elsewhere across the discussion waters. Scattered showers and isolated thunderstorms are found offshore Colombia. For the forecast, moderate to rough seas from swell generated by the Gulf of Tehuantepec gale-force gap wind event will subside well offshore of Guatemala through the rest of today. Winds will pulse moderate to fresh, locally strong, near the Gulf of Papagayo at night through Thu night. Gentle to moderate winds will prevail south of the monsoon trough. Seas may build slightly in SW swell offshore Ecuador to the Galapagos Islands by the end of the week into the weekend, then build across the waters from W to E by the end of the weekend as NW swell arrives. Looking ahead, a broad area of low pressure has formed several hundred nautical miles south of the Gulf of Tehuantepec but is only producing a few disorganized showers and thunderstorms. Gradual development of this system is expected, and a tropical depression is likely to form late this week or over the weekend while the system meanders or drifts northwestward over the far eastern portion of the basin. This system has a low chance of tropical cyclone development in the next 48 hours, and high chance through 7 days. ...REMAINDER OF THE AREA... Please see the SPECIAL FEATURES section above for more details on Tropical Storm Norma, and for details on a large NW swell event over the NW waters. High pressure centered N of the area extends a ridge through 30N133W to near the Revillagigedo Islands. Light winds are over the far NW waters. Gentle to moderate winds are elsewhere over the discussion waters. As described above, large NW swell is propagating across the NW waters bringing seas of 8-14 ft N of 10N and W of 130W, highest near 30N140W, with a separate area of N to NW swell propagating across the waters N of 23N between 119W and 130W. Elsewhere, seas of 5-7 ft prevail, reaching to around 8 ft S of the Equator to 03.4S to the W of 105W. For the forecast, other than the large NW swell event, Norma will strengthen to a hurricane near 15.8N 108.1W this evening, move to 16.9N 108.3W Thu morning, 17.8N 108.5W Thu evening, 18.7N 109.0W Fri morning, 19.6N 109.5W Fri evening, and 20.8N 109.9W Sat morning. Norma will change little in intensity as it moves to 21.9N 109.9W early Sun. Mainly gentle to moderate winds under a weak pressure pattern will prevail elsewhere across the open waters through the next several days. $$ Lewitsky