000 AXPZ20 KNHC 080916 TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Fri Jun 8 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 0600 UTC surface analysis and satellite imagery through 0900 UTC. ...SPECIAL FEATURES... Hurricane Aletta centered near 15.8N 110.7W at 0900 UTC, about 240 nm S of Socorro Island, moving WNW or 300 deg at 5 kt. Maximum sustained winds are 105 kt with gusts to 130 kt. Minimum central pressure is 957 mb. Satellite imagery shows that Aletta has rapidly intensified, with an eye and well defined central dense overcast. Numerous moderate to strong convection is within 120 nm of the center. Scattered moderate isolated strong convection is occurring within 210 nm NE and 180 nm SE of the center. Aletta is expected to continue to strengthen during the next 12 hours, with its maximum winds reaching 115 kt with gusts to 140 kt later today. Aletta is then forecast to be impacted by vertical shear, and begin to weaken afterwards. 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. A tropical wave is along 97W north of 08N extending inland across southern Mexico west of the Gulf of Tehuantepec, moving west at 10 kt. The southern part of the wave is enhancing deep convection associated with the monsoon trough. The wave will move further west during the next 24 hours, with an area of low pressure expected to form along it near 10N98W on Sat. Model guidance indicates that environmental conditions will become favorable for this system to develop into a tropical cyclone this weekend. There is a high potential for development during the next two days. Fresh easterly flow behind this system is expected to increase to strong 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. Please refer to the latest NHC Tropical Weather Outlook under header ABPZ20/MIATWOEP for the latest potential for development on this system. ...INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough axis extends from northern Colombia across southern Costa Rica to 09N84W to 11N96W, where it has fractured by Hurricane Aletta. It then resumes from 13N115W to 07N129W, where the ITCZ continues to beyond 06N140W. Scattered moderate isolated strong convection is from 08N to 15N between 90W and 105W, and also from 09N to 12N between 116W and 120W. ...DISCUSSION... OFFSHORE WATERS WITHIN 250 NM OF MEXICO... A broad ridge extends from a 1026 mb high centered near 30N138W southeastward to near Islas Revillagigedo. A low pressure trough will remain over the Baja Peninsula and the Gulf of California through Sat. This pressure pattern will support moderate to fresh northwest winds west of the Baja Peninsula throughout the day. 6 to 8 ft seas are expected N of 25N as a new pulse of NW swell expands in areal coverage during the next few days. Gulf of California: light to gentle southerly winds expected to continue through the weekend. Gulf of Tehuantepec: a brief period of fresh to strong northerly winds will flow across the Gulf of Tehuantepec later today as a cyclonic circulation develops from the tropical wave described above affects the area downstream from the region this weekend. OFFSHORE WATERS WITHIN 250 NM OF CENTRAL AMERICA, COLOMBIA, AND WITHIN 750 NM OF ECUADOR... Fuego Volcano in Guatemala may vent some ash in the coming days, but remains relatively quite since its major eruption last Sun. Moderate to locally fresh nocturnal drainage flow across and downstream of the Gulf of Papagayo will be prolonged through Sat as a tighter pressure gradient develops behind the tropical wave presently along 97W. The monsoon trough will meander across the forecast waters near 10N. Gentle to moderate easterly winds are expected elsewhere north of the monsoon trough, with gentle to moderate southwest winds south of the trough axis through Sat. SW cross-equatorial swell will sweep into regional waters this weekend, increasing seas to 6-8 ft by Sunday. REMAINDER OF THE AREA... The surface ridge extending across northern waters will slowly shift westward the next few days. Fresh trades will continue across the tropics to the south of the ridge. Model guidance indicates that these winds increase in areal coverage later today as the Aletta tracks generally west to northwestward. NW to N swell from strong northerly winds along the coast of California will increase seas to around 8 ft N of 28N between 117W and 122W today, then reach south to near 24N between 117W to 124W on Sat, with max wave heights to 9 ft. Long period cross-equatorial SW swell will build seas west of 100W to 8 ft this morning. As the SW swell propagates northward and merges with swell associated with Aletta this weekend, a very large area of 8 ft or greater seas will expand to include almost all of the basin south of 24N between 100W and 135W by Sunday. Seas are expected to become somewhat chaotic in mixed swell as the weekend progresses, especially near Aletta. $$ Mundell