000 AXPZ20 KNHC 070356 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 0405 UTC Thu Jun 7 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 0000 UTC surface analysis and satellite imagery through 0230 UTC. ...SPECIAL FEATURES... Tropical Storm Aletta is centered near 14.3N 108.4W at 0300 UTC, moving W or 275 deg at 6 kt. Maximum sustained winds have increased to 45 kt with gusts to 55 kt. Minimum central pressure is estimated at 999 mb. Latest satellite imagery shows numerous strong thunderstorms continuing to develop across the NE semicircle, where the strongest winds are found. Scattered to numerous strong convection is located within 180 nm NE, 90 nm SE, 0 nm SW, and 120 nm across the NW quadrants of Aletta. A tail of trailing scattered moderate to strong convection to the SW of the center is found from 09.5N to 12.5N between 108W and 116W. A westward motion will continue through Thu, then become more of west-northwestward motion through the upcoming weekend. The cyclone is forecast to strengthen to a minimal hurricane strength late Fri evening as it moves over very warm sea surface temperatures and under favorable upper-level conditions. Very strong convection is expected to persist across the south and southeast periphery of this system through Fri. Please refer to the latest NHC Forecast Advisory under WMO/AWIPS headers WTPZ22/MIATCMEP2, and the NE Pacific High Seas Forecast under WMO/AWIPS headers FZPN03/MIAHSFEP2 for the latest information on this system. ...TROPICAL WAVES... A tropical wave axis is along 93W-94W north of 08N to inland Mexico, moving westward at 10-15 kt. The southern part of the wave is helping to enhance deep convection occurring to the south of the monsoon trough as described above. Scattered moderate to strong convection is seen over much of southern and central Guatemala extending southeast across the mountainous terrain to western Honduras and El Salvador. The wave is forecast to move slowly westward during the next 48 hours, at which time low pressure is expected to form along it near 10N98W. Fresh easterly flow behind this system is expected to increase to strong Fri through Sat, with some chance of these winds increasing further as the low pressure deepens. This tightening of the gradient will bring fresh northeast to east winds across the Gulf of Papagayo region through the upcoming weekend. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from a 1009 mb low that is near 09.5N73W TO 10N80W TO 08N89W TO 12N102W, where it has fractured from Tropical Storm Aletta. It then resumes at 11N112W TO 07N124W, where the ITCZ then continues to beyond 07N140W. Scattered moderate to strong convection is noted within 210 nm N and 150 nm S of the trough between 79W and 102W, and within 150 nm N and 90 nm S of the ITCZ to the west of 131W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A broad ridge extends from a 1024 mb high pressure system centered near 31N139W southeastward to near the Islas Revillagigedo. The typical low pressure trough will remain over the Baja Peninsula and Gulf of California through Fri. This pressure pattern will generally support moderate to fresh northwest winds west of the Baja Peninsula through Fri. Seas of 4-7 ft this evening are forecast to build to 6-8 ft beginning on Thu due to a new pulse of NW swell, with the swell forecast by guidance to expand in areal coverage through the next few days. Inside the Gulf of California, generally light to gentle southerly wind flow is expected to continue through the weekend. Afternoon to evening sea breezes are forecast to dominate the Gulf for the next few days and will freshen the winds to around 20 kt along the coasts each day. Variable light to gentle winds are expected across the Gulf of Tehuantepec through Thu night, then a brief episode of fresh to strong northerly winds will flow across the Gulf of Tehuantepec Fri as a cyclonic circulation associated with a tropical wave as described above begins to impact the waters downstream from the Gulf of Tehuantepec through most of Fri according the latest model runs. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Fuego Volcano in Guatemala may resume venting some ash in the coming days, but remains relatively quite since the major eruption this past Sunday. Moderate to locally fresh nocturnal drainage flow across and downstream of the Gulf of Papagayo will be prolonged through Fri as a tighter pressure gradient develops behind a tropical wave, presently along 93-94W, keeps these winds mostly in the fresh range. The monsoon trough will meander across the forecast waters near 10N. Gentle to moderate E winds are generally forecast elsewhere north of the monsoon trough through Thu night. Gentle to moderate southwest winds are forecast south of the monsoon trough through Sat. SW cross equatorial swell will move into the regional waters over the upcoming weekend and raise seas to 6-8 ft by Sunday. REMAINDER OF THE AREA... The surface ridge extending across the northern waters will gradually shift W during the next few days. Fresh trades will continue across the tropics to the south of the ridge, generally from 08N to 18N west of 125W through Fri. Model guidance indicates that these winds increase in coverage late Fri as the Aletta tracks in a general northwesterly motion. NW to N swell producing seas to around 8 ft propagating through the northeast waters N of 29N between 118W and 125W will gradually subside overnight, then a new pulse of NW to N swell will propagate into the same waters beginning early on Thu afternoon, and reach south to near 26N between 117W-124W on Fri bringing seas to around 8 ft. Long period cross equatorial SW swell will build seas near the Equator between 99W and 125W to 8 ft by tonight. The long period SW swell will continue to propagate northward and merge with swell associated with Aletta by Fri, with expected seas in the 8- 10 ft range. The area of 8 ft seas will impressively expand to include almost all of the basin to the south of 22N between 105W and 136W during this time frame. $$ Stripling