968 AXPZ20 KNHC 222205 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 2205 UTC Sun Jul 22 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 2145 UTC. ...TROPICAL WAVES... A low-latitude tropical wave has its axis along 79W N of 01N, moving westward at about 15 kt. The wave is evident in tropical wave model diagnostics as well as a maximum in total precipitable water satellite imagery. Scattered moderate isolated strong convection quickly developed this morning and continues east of the wave north of 07N to over much of Panama where the eastern segment of the monsoon trough is found. A tropical wave has its axis along 92W/93W north of 04N to inland far southeastern Mexico, moving westward at 10-15 kt. The wave is evident in 700 mb model guidance streamlines as well as a very pronounced maximum in total precipitable water satellite imagery. Numerous moderate to strong convection is occurring from 10N-13N between 94W-98W. Scattered moderate isolated strong convection is seen where the wave intersects the monsoon trough within 180 nm west of the wave from 06N-09N, and also within 60 nm of 11N94.5W. Little development is expected of this wave over the next couple of days. A tropical wave has its axis extending from 06N121W to newly formed low pressure near 10N123W 1010 mb and to 19N121W, moving westward 15-20 kt. The wave is associated with broad troughing at 700 mb as depicted in model guidance. Scattered moderate isolated strong convection is seen from 10N-14N east of the wave to 116W, and also from 10N-13N west of the wave to 124W. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from a 1010 mb low over northwestern Colombia near 10N75W to 10N85W to 10N94W to 11N105W to 11N115W to weakening low pressure of 1009 mb at 13N140W. Aside from convection associated with the tropical waves, scattered moderate isolated strong convection is within 240 nm south of the axis between 80W-89W, within 180 nm south of the axis between 122W-129W, within 180 nm south of the axis between 133W and 136W, within 120 nm south of the axis between 100W and 103W and within 60 nm of the axis between 107W-110W. Scattered moderate convection is within 180 nm south of the trough between 94W-99W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... The southeastward extent of rather weak high pressure ridging that enters the region well beyond 250 nm of the Mexican coast is analyzed near the Revillagigedo Islands near 16N106W. The ridge is maintaining light to moderate NW winds across the Mexican offshore waters, except for the Gulf of Tehuantepec area as discussed below. Little change is expected in these conditions during the next several days. A long period SW cross-equatorial swell is affecting the waters S of 15N. This extensive swell event will continue spreading northward, and will cause seas to build to the range of 7-9 ft in the open waters for all the forecast zones through Tue night. Gulf of Tehuantepec: the fresh to strong north winds indicated by the 1614Z Ascat pass will shrink in coverage this evening, but are expected to again pulse over through the gap late tonight through Mon morning before diminishing to light to moderate early Mon afternoon and gentle S to SW winds Mon night and gentle variable winds Tue. Wind waves generated by the north winds are interacting with the SW swell event resulting in mixed seas south of the Gulf, with wave heights maxing out to 9 ft. These wave will slowly lower to 8 ft during Mon, then subside slightly during Tue and into Wed. 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 Wed morning before diminishing to fresh intensity. Seas from these NE to E winds will interact with the SW swell event to produce mixed seas in the Gulf as high as high as 10 ft on Mon before seas begin to slowly subside on Tue. Northeast to east winds of only moderate speeds or weaker are forecast elsewhere N of the monsoon trough which will meander west of Central America between 07N-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 to the south of the equator have build to 9 ft. Seas will peak between 8-10 ft on Mon in the open waters, with the highest seas expected to the west of Ecuador. REMAINDER OF THE AREA... A surface ridge extends east-southeastward from 32N140W to 24N125W and to near the Revillagigedo Islands near 16N106W. Weak low pressure of 1016 mb is analyzed at 32N129W, with a trough to near 25N130W. Widely scattered showers and isolated thunderstorms are noted north of 30N and between 131W-135W. The low will move in a westerly motion through Tue while weakening. It is expected to weaken to a trough from 32N139W to 29N141W by Wed. The gradient between the ridge and lower pressure to its south in the sub-tropics and tropics is maintaining mainly moderate trade winds north of the monsoon trough south of 20N and west of 115W. Little change in this pattern is expected for the upcoming week. Swell producing waveheights to a maximum of 8 ft generated by strong winds N of the area is propagating southward encompassing the discussion waters N of 29N between 130W-138W. This swell will continue to affect this region while slowly shifting westward and subsiding through Mon evening. Newly formed low pressure of 1010 mb is along the tropical wave that extends from 06N121W to 19N121W. Fresh to strong winds are present within 60 nm of low in the E and SE quadrants per the 1756Z Ascat pass, with seas of 8-10 ft. Fresh winds are elsewhere within 120 nm over the E and SE quadrants and within 150 nm of the low remainder quadrants. The low is forecast to move in a west-northwest motion through the next 24 hours, then in west-northwest motion afterwards reaching to near 12N 132W by early Wed afternoon. Fresh to strong winds are forecast from 12N- 15N between 131W-134W, with seas of 8-10 ft by Wed. A 1009 mb area of low pressure is centered at 13N140W, moving westward around 15 kt. Fresh to strong winds northeast to east are occurring from 14N to 17N west of 139W, with associated seas in the range of 8 to 10 ft. Scattered moderate convection is seen within from 11.5N to 13N west of 136W. Scattered moderate isolated strong convection is present from 10N to 11.5N west of 136W. This low will shortly cross 140W, however, the gradient between it and the high pressure to its north will be tight enough to allow for fresh northeast to east winds from 14N-19N west of 138W through early Mon along with seas of 8-9 ft in mixed E and SE swell. These swells will gradually decay by late Mon night allowing for the seas to lower below 8 ft. Large long-period SW swell is crossing the equator, with seas of 8 to 10 ft extending from the Southern Hemisphere northward to a line from 03.4S83W to 00N86W to 12N103W to 14N123W to 04N137W, as confirmed by satellite-derived sea height data received this afternoon. The swell will continue to propagate northward and allow for seas to build to 8 ft or above across most of the area to the south of 25N and east of 133W on Mon. The swell will decay allowing for the seas to subside and seas subside Tue through Wed. $$ Aguirre