AXPZ20 KNHC 280948

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
1005 UTC Thu Jul 27 2017

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 0815 UTC.


Recently downgraded Tropical Storm Hilary is located near 18.7N 117.9W at 0900 UTC, or about 5155 nm WSW of the southern tip of Baja California, moving WNW at 7 kt. Estimated minimum central pressure is 992 mb. Maximum sustained wind speed is 60 kt with gusts to 75 kt. Numerous moderate convection is within 60 nm of the center. Hilary is forecast to continue moving WNW and weaken slowly over the next 48 hours before weakening more rapidly by 72 hours as it reaches cooler waters. See latest NHC forecast/ advisory under AWIPS/WMO headers MIATCMEP4/WTPZ24 for more details.

Tropical Storm Irwin is centered near 14.9N 124.8W at 0900 UTC, or about 975 nm WSW of the southern tip of Baja California, moving W at 2 kt. Estimated minimum central pressure is 1001 mb. Maximum sustained wind speed is 45 kt with gusts to 55 kt. Numerous moderate and scattered strong convection are within 90 nm north and 120 nm south of the center. Some modest fluctuations in intensity below hurricane force are expected during the next 48 hours, or more, before Irwin interacts with Hilary and begins to weaken considerably. See latest NHC forecast/ advisory under AWIPS/WMO headers MIATCMEP5/WTPZ25 for more details.


A tropical wave is analyzed along 94W-95W, north of 10N, moving W at 10-15 kt. Isolated moderate convection is within 180 nm east of the wave axis.

A tropical wave is analyzed along 110W-111W, north of 07N, moving W at 5-10 kt. Scattered moderate convection is from 06N to 15N between 107W and 116W.


The monsoon trough extends across Costa Rica near 10N84W to 08N95W to 09N105W to 13N112W, and resumes west of the tropical cyclone activity near 11N130W to 08N137W. The ITCZ axis extends from 08N137W to beyond 07N140W. Aside from convection associated with the tropical waves, scattered moderate isolated strong convection is from 05N to 10N between 89W and 104W, and from 03N to 10N, east of 85W. Scattered moderate convection is within 90 nm of the monsoon trough and ITCZ axis, west of 130W.



High pressure centered northwest of the area will support gentle to moderate NW winds within 120 nm of the Baja California peninsula through Saturday. Seas of at least 8 ft associated with tropical cyclone Hilary will continue to impact the offshore zones of Baja California through the upcoming weekend. As Hilary moves away from this area, a ridge axis will fill in between the departing storm and Baja California, resulting in moderate to fresh NW winds developing Sunday through early next week.

Nocturnal fresh northerly winds are forecast across the Gulf of Tehuantepec through this morning with seas peaking around 8 ft. Cross equatorial long period southerly swell with seas of 7 to 8 ft will reach the offshore waters between the Gulf of Tehuantepec and Cabo Corrientes on Sun, and the waters between Los Cabos and Cabo Corrientes on Mon. Elsewhere, generally moderate NW winds and seas of 5 to 7 ft will prevail.


Across the Gulf of Papagayo, expect fresh winds to develop tonight and again Saturday night with the assistance of the nocturnal drainage flow, building maximum seas of 7 to 8 ft in a mix of E wind waves and long period SW swell.

Otherwise, gentle to moderate S to SW winds are expected the next few days. Strong long period cross-equatorial SSW swell will continue to propagate into the forecast waters through Saturday, with seas 8 to 9 ft reaching as far north as 10N later today. The area of 8 ft seas will then reach just offshore all central America Pacific coastal sections by Sunday.


High pressure is located N of the area with a ridge axis extending across the northern forecast waters N of 20N. The pressure gradient between this system and the active zone of tropical cyclones will maintain moderate to fresh N to NE winds W of 120W through Saturday. Long period cross equatorial SW swell of 8 to 9 ft will spread across the waters S of 10N and E of 110W, persisting through Sunday night. As the tropical cyclone activity shifts to the NW over our waters later this weekend, a weak pressure pattern will develop between the cyclones and the equatorial trough to the south. This will result in a broadening area of gentle to moderate winds between 10N and 20N, west of 115W early next week.

$$ Latto/Stripling