AXPZ20 KNHC 202117

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
2205 UTC Sun May 20 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 2000 UTC.


The monsoon trough extends from 10N74W TO 09N81W TO 11N86W TO 10.5N126W TO 09.5N130W. The ITCZ continues from 09.5N130W to beyond 07.5N140W. Scattered moderate to strong convection is noted from 04.5N to 10.5N to the east of 109W, from 06.5N to 11.5N between 110W and 123W, and from 09N to 12N between 123W and 133W.



Moderate to fresh NW winds continue across the offshore waters of Baja California this afternoon, and are maintaining seas of 5 to 7 ft across these waters. Generally light to gentle variable winds are noted over the Gulf of California, except for moderate southerly winds across far N portions. Light NW to W winds are noted farther south across the Mexican coastal waters. The main forecast issue ahead will be the onset of long period SW swell moving into the open Pacific waters off Mexico late this afternoon and evening. Large SW swell will reach waters of southern Mexico by early Mon, and into the open waters off Baja California Mon night and Tue, mixing with NW swell off Baja California Norte. Seas across the region will build to 7-8 ft in this mixed swell by Mon afternoon and spread into the mouth of the Gulf of California early Tue.

In the Gulf of Tehuantepec, light winds will persist into Tue, then moderate to fresh gap winds will pulse briefly as sharp troughing shifts slowly NW across southeast Mexico.


Gulf of Papagayo: Light to gentle winds will dominate the gulf the entire forecast period as weak pressure will prevail across Central America. Seas of 5-8 ft are forecast over the Gulf and nearby waters through mid week due to the strong long period SW swell expected to arrive tonight.

Gulf of Panama: Gentle to moderate S to SW winds are forecast through Wed with seas of 4-6 ft in long period SW swell, building to 5-7 ft on Mon as the swell reaches the coasts of Panama and Colombia.

Elsewhere, gentle to moderate SW winds are expected to the south of the monsoon trough with light to gentle variable winds north of trough as a weak pressure pattern remains over Central America. Seas of 6-7 ft in building long period SW swell west of the Galapagos Islands are expected to propagate northward tonight through late Tue next week, building to 8 to 9 ft to the west and northwest of the Galapagos Islands tonight through Mon night.


A ridge extends from 1028 high pressure centered near 32N141W through the Revillagigedo Islands. The ridge is supporting moderate to fresh trade winds farther south into the deep tropics north of the monsoon trough and ITCZ. Convergence of the moderate to fresh NE trades with light to moderate SW flow on the south side of the monsoon trough is supporting clusters of showers and thunderstorms near the monsoon trough west of 112W. Various recent altimeter satellite passes indicate 4 to 6 ft seas north of 20N where winds are lighter, and 7 to 9 ft seas in the trade wind belt between the monsoon trough as far north as 17N as SW swell has begun to move into the region.

The ridge will build north of 20N through early in the week, enhancing trade winds especially near a developing weak low pressure along the monsoon trough near 10N134W. A new round of SW swell in excess of 8 ft is noted south of 10N, propagating northward. This will overtake the region east of 130W late this afternoon through Tue. Looking ahead, the upper pattern will amplify by mid week, supporting development of another weak low along the monsoon trough west of 125W.

$$ Stripling