AXPZ20 KNHC 291633

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1605 UTC Tue Sep 29 2020

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 1540 UTC.


Tropical Depression Eighteen-E is centered near 13.3N 108.5W at 1500 UTC moving W at 9 kt. Estimated minimum central pressure is 1005 mb. Maximum sustained wind speed is 30 kt with gusts to 40 kt. Scattered moderate to strong convection is noted from 10N to 20N between 103W and 116W. The system is forecast to steadily intensify as it moves on a westward to west-northwestward track during the next several days. The current forecast has the depression becoming a tropical storm this evening just outside of the offshore waters near 13.8N 110.4W, then continuing WNW, and reaching hurricane intensity Wednesday evening. Please read the latest NHC Public Advisory at https://www.nhc.noaa.gov/text/MIATCPEP3.shtml and Forecast/ Advisory at https://www.nhc.noaa.gov/text/MIATCMEP3.shtml for more details.

Gulf of Tehuantepec gale warning: A strong gale force gap wind event is expected across the Gulf of Tehuantepec late today through Fri night as cold front moves across the Gulf of Mexico. The pressure gradient between high pressure building behind the front and the eastern Pacific monsoon trough will tighten over the area. This will increase winds funneling through the Chivela Pass into the Gulf of Tehuantepec. Winds will rapidly increase to gale force by late this afternoon, reaching 30-40 kt by tonight. At that time, seas will build to 15-18 ft. Swell generated from this event are forecast to reach 100W on Wed. Please read the latest NWS High Seas Forecast issued by the National Hurricane Center at website https://www.nhc.noaa.gov/text/MIAHSFEP@.shtml for more details.

Of note, the 20-year climatology of the Tehuantepec gap wind events indicates that on average 16 gale-force events and 5 storm force-events occur in the Gulf of Tehuantepec each cold season. Most gale-force events occurred during November and December, while most storm-force winds occurred in January. Based on latest model trends and the present evolving synoptic scale setup, this forecast event most likely will supersede the previously recorded earliest start date of October 3rd.


The monsoon trough extends from 10N74W to 10N84W to T.D. EIGHTEEN-E NEAR 13.3N108.5W to 09N140W. Scattered moderate isolated strong convection is noted from 03N to 11N between 78W and 96W and within 120 nm S of trough between 127W and 140W.


Please see above for more on the Gulf of Tehuantepec gale force gap wind event.

Elsewhere, a weak ridge west of Baja California will maintain gentle to moderate NW to N winds across the region for the next few days. Gentle to moderate northerly winds will prevail across the northern Gulf of California through tonight while mainly light to gentle winds are expected elsewhere across the Gulf most of the forecast period. Elsewhere, light to gentle winds are generally expected across the waters from Las Tres Marias Islands to Puerto Angel for the next several days. T.D. Eighteen-E is expected to become a large hurricane. The size of the system will generate a large area of seas greater than 8 ft spreading from swell out and away the cyclone center. This south swell will spread across the offshore waters west of the Baja California peninsula Thu into the weekend.


Moderate southerly flow prevails S of the monsoon trough, with gentle winds north of the monsoon trough. Combined seas are currently 5 to 7 ft in a mix of wind waves and southerly swell. Long period SW swell is moving over the waters between Ecuador and the Galapagos Islands, with seas to 8 ft. These seas will subside below 8 ft tonight. Seas generated by the gap wind event in the Tehuantepec region will propagate across the offshore waters of Guatemala and El Salvador beginning on Wed morning.


Please see Special Features section above for newly developed T.D.Eighteen-E.

Outside of T.D. Eighteen-E, a weak pressure gradient prevails with light to gentle winds prevailing N of the monsoon trough, and gentle to moderate winds S of the monsoon trough. The cross equatorial swell across the waters S of 15N has started to subside, with seas in the 6-8 ft range. These seas will continue to subside trough the middle of the week. New NW swell will propagate into the NW waters the middle of the week. Seas will build to 9 ft over the far NW waters by Wed night. T.D. Eighteen-E is expected to become a large hurricane. The size of the system will generate a large area of seas greater than 8 ft spreading well away from the cyclone center. By Saturday, seas greater than 8 ft will cover much of the waters N of 10N and W of 115W.

$$ Stripling