000 AXPZ20 KNHC 161004 RRA TWDEP Tropical Weather Discussion NWS National Hurricane Center Miami FL 1005 UTC Thu Jun 16 2016 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... A weak and broad 1010 mb low pressure center is near 15.5N 105.5W, embedded in the monsoon trough. The low center is moving to the west-northwest about 5 knots. Convective precipitation: scattered to numerous strong within 120 nm of the center in the northeastern quadrant, and within 180 nm of the center in the southeastern quadrant. scattered moderate to isolated strong within 90 nm of the center in the southern semicircle. Scattered moderate to isolated strong from 18N to 21N between 103W and 108w. The precipitation that was comparatively closer to the center 6 hours ago eventually weakened and dissipated. Only during the last few hours has the scattered moderate to isolated strong precipitation developed at a closer distance to the center. the comparatively strongest precipitation still is within 120 nm from the center to the northeast, and within 180 nm of the center to the southeast. The wind speeds that are closer to the center still are light to moderate. It is possible that a swath of fresh to strong winds may be possible on the northeastern side of the low center, well removed from the center. This may happen due to the funneling effects up against the coast of southwestern Mexico. The combined sea heights of 8 feet to 9 feet also surround the low center. The low has a medium potential to develop into a tropical cyclone during the next 48 hours. ...TROPICAL WAVES... A tropical wave is along 85W/86W from 18N southward, moving westward 15 to 20 knots. The wave extends from the northwestern part of the Caribbean Sea and eastern Gulf of Honduras, through central sections of Honduras, western sections of Nicaragua, and off the coast of northwestern Costa Rica. No significant deep convective precipitation accompanies the wave at this moment. ..INTERTROPICAL CONVERGENCE ZONE/MONSOON TROUGH... The monsoon trough extends from the 1010 mb low pressure center, that is the subject of the Special Features section, to 12N110W, to 10N114W, to 09N120W, to 08N125W. The ITCZ continues from 08N125W to 07N130W 07N132W 08N134W, and 07N140W. A surface trough is along 11N132W 08N135W 05N137W. Convective precipitation: Scattered moderate to strong within 120 nm to the north of the monsoon trough, and within 90 nm to the south of the monsoon trough, between 109w and 124w. Scattered moderate to isolated strong within 180 nm to the north of the ITCZ from 128W westward, and within 90 nm to the south of the ITCZ from 133W westward. A 1014 mb low pressure center is near 09N95W. Convective precipitation: Scattered strong from 06N to 08N between 98W and 100W. Scattered moderate to isolated strong elsewhere from 04N to 06N between 91W and 95W, and from 06N to 09N between 96W and 98W. ...DISCUSSION... From 15N northward and from 120W eastward: A surface ridge is along 22N115W to 27N123W beyond 29N140W. A 1010 mb low pressure center is near 15N, and it is described in great detail in the special features section. The surface ridge will retract from southeast to northwest through Friday, as the low pressure area advances across this part of the area. The numerical models indicate that mainly moderate winds will prevail through the remainder of the week, except occasionally pulsing to fresh offshore of the Baja California peninsula during the next several days. Combined seas of 5 to 7 feet will build to 7 to 9 feet to the north of 28N and to the west of the Baja California peninsula tonight through early Friday, then subsiding to 5 to 7 feet through Saturday. The surface pressure gradient that exists to the northwest of the area will tighten later this weekend, allowing for fresh northwest swell to arrive again and build combined seas to 7 to 9 ft by late Saturday night through Monday, subsiding Monday night through the middle of next week. The Gulf of California: A surface trough will linger from northwest to southeast across the Gulf resulting in variable winds depending on either side of the trough. The wind speeds will be light to moderate, with seas generally 2 feet or less away from the entrance of the Gulf. Little change is forecast during the rest of the week, and continuing into the middle of next week. The Gulf of Tehuantepec: Mainly light onshore flow is anticipated, shifting to offshore during the overnight hours with nocturnal drainage flow through Friday, and sea heights of 5 to 7 feet, subsiding to 4 to 6 feet late Thursday night. Offshore nocturnal flow is forecast to increase to fresh by late Friday night into early Saturday morning, then increase to fresh to strong late Saturday night into early Sunday morning as the local pressure gradient tightens. Similar conditions are then forecast for the following several nights/early morning hours. These increasing winds will build the sea heights temporarily to 7 to 10 feet. From 15N southward and from 120W eastward: The 1010 mb low pressure center that is near 15N105W will move gradually west-northwest out of this area. expect mainly gentle to moderate winds on either side of the monsoon trough, elsewhere, with primarily a westward/onshore component, except during the overnight hours when nocturnal drainage flow will result in offshore winds. Winds are forecast to increase to fresh to strong offshore of the Gulf of Papagayo late Monday night into early Tuesday as trades increase east of Central America in the western Caribbean Sea. These increasing winds will build seas locally to 6-9 feet by Tuesday morning. Cross-equatorial southwesterly swell will continue to propagate to the northeast with combined seas of 6 to 9 feet through tonight, subsiding thereafter. A new set of southwesterly swell will arrive at the equator and 120W by early Sunday, propagating to the northeast through early next week, with another and more significant southwesterly swell train arriving by the middle of next week. This quickly arriving reinforcing set of swell may build combined seas up to 8 to 12 feet by Wednesday afternoon. Elsewhere to the west of 120W: A surface ridge remains in the northern waters. The difference in pressure between the ridge and the lower pressure in the vicinity of the intertropical convergence zone will maintain moderate to fresh trade winds to the north of the ITCZ through Thursday afternoon. The surface ridge will then weaken Thursday night into Friday as a weak cold front or remnant trough slips into the far northern waters. This front/trough will stall in the far northwest portion by Friday morning, then will gradually retreat westward through Saturday, finally moving to the west of 140W Saturday night as ridging rebuilds from the north-northeast. As this ridging rebuilds, winds offshore of southern California will increase to fresh to strong due to the tightening pressure gradient. These winds will send fresh northerly swells into the area to the north of 25N and to the east of 130W Sunday through Monday. The ridging is then forecast to weaken and shift westward as broad troughing develops to the west of the Baja California peninsula by the middle of next week. $$ MT