077 AXPZ20 KNHC 212146 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2145 UTC Sat Jul 21 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 2100 UTC. ...TROPICAL WAVES... A tropical wave is analyzed with an axis from 04N83W to 23N83W, moving westward at around 15 to 20 kt. The wave is evident in 700 mb streamlines in model guidance as well as a maximum in total precipitable water satellite imagery. Scattered moderate and isolated strong convection are noted from 04N to 12N E of 91W. A tropical wave is analyzed with an axis from 06N112W to 18N112W, moving westward at around 15 to 20 kt. The wave is associated with troughing at 700 mb in model guidance as well as a maximum in total precipitable water satellite imagery. Scattered moderate and isolated strong convection is present from 05N to 14N between 108W and 116W. A tropical wave is analyzed with an axis from 02N121W to 12N121W, moving westward at around 15 to 20 kt. The wave is weak, but can be tracked with subtle 700 mb troughing in model guidance. Scattered moderate convection is observed from 07N to 14N between 116W and 125W. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from 09N79W to 08N100W to 10N125W. The ITCZ continues from 10N125W to 13N132W. Aside from convection associated with the tropical waves, scattered moderate and isolated strong convection are from 05N to 13N between 91W and 107W, and from 07N to 18N between 125W and 130W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A surface ridge extends SE from 26N124W to near the Revillagigedo Islands. The ridge is maintaining light to moderate NW winds across the Mexican offshore waters, except for the Gulf of Tehuantepec discussed below. Little change is expected in these conditions during the next several days. A long period SW cross- equatorial swell is crossing the waters S of 15N. The extensive swell event will continue spreading N and will cause seas to build to between 7 and 9 ft in the open waters for all the forecast zones through early next week. In the Gulf of Tehuantepec, pulses of fresh to strong N gap winds will occur during the late night and morning hours until Mon morning. Wind waves generated by these N winds will interact with the SW swell event to produce mixed seas south of the Gulf peaking near 10 ft on Sun before winds subside on Mon morning. Seas near the Gulf of Tehuantepec will remain above 8 ft until Wed morning as SW swell continue to arrive. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Gulf of Papagayo: Fresh to strong easterly winds will pulse during the late night and morning hours through early next week. Seas from these easterly winds will interact with the SW swell event to produce mixed seas SW of the Gulf up to 10 ft Mon before fading on Tue. Easterly winds of only moderate or weaker are forecast elsewhere N of the monsoon trough which will meander west of Central America between 07N and 10N. Moderate to fresh S to SW winds are generally expected S of the trough axis during the next several days. A long-period SW cross-equatorial swell event is already affecting the region as seas S of the equator have risen to 8 ft. Seas will peak between 8 and 10 ft on Mon in the open waters, with the highest seas expected W of Ecuador. A low latitude tropical wave crossing S America may reach the waters S of 07N by Sun, enhancing shower and thunderstorm activity over the region. REMAINDER OF THE AREA... A broken surface ridge in place from 30N140W to 26N132W, then from 26N124W to the Revillagigedo Islands is maintaining mainly moderate trade winds N of the monsoon trough, S of 18N and W of 115W. Little change in this pattern is expected for the next several days. Swell to 8 ft generated by strong winds N of the area is propagating S to cover the discussion waters N of 29N between 128W and 136W. This swell will prevail over this region while slowly shifting westward through Mon. A 1008 mb area of low pressure is centered near 13N134W. Fresh to locally strong winds are occurring within about 300 nm N of the low center with seas to 9 ft. Scattered moderate and isolated strong convection are occurring from 06N to 13N between 130W and 140W. This low and associated conditions will move W of the discussion area by Mon. Large long period SW swell is crossing the equator, with seas of 8 to 10 ft extending from the equator northward to a line from 05N93W to 13N106W to 13N121W to 03N139W, as confirmed by recent satellite altimeter passes. The swell will continue to propagate N and bring seas of 8 ft or above to most of the area S of 25N east of 133W Mon, before the swell decay and seas subside on Tue. $$ Latto