| Current Conditions | ||
| Temp |  | 2.8 C |
| RH | | 24 % |
| Wind | | N 17 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 173 FXHW60 PHFO 201409 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 409 AM HST Sat Jul 20 2019 .SYNOPSIS... A high pressure ridge will remain north of the Hawaiian Islands into the middle of next week. Expect moderate to breezy trade winds through the period with showers favoring windward and mountain areas. Additional moisture may move up from the deep tropics from early Monday morning into Tuesday, possibly increasing showers across the Big Island and Maui. More typical trade wind weather returns from Wednesday onward. && .DISCUSSION... A trade wind weather pattern will continue into the first half of next week as a high pressure ridge remains locked in place north of the islands. Regional infra-red satellite imagery shows a fairly active convergence zone around 10 degrees north latitude just south of the state. Cloud bands with embedded showers are slowly drifting in with the trade winds. A seasonably deep upper level low also appears on water vapor satellite imagery roughly 500 miles north of Kauai. Large scale lift and instability associated with this upper low continues to weaken the stable subsidence inversion over the islands allowing deeper clouds to form and more shower activity mainly along windward and mountain slopes in the overnight through early morning hours through Sunday. Brief periods of showers are possibly over leeward slopes with stronger shower bands, especially in the overnight to early morning hours. Global models continue to show a weak trough developing south of the Big Island this weekend. Both the American (GFS) model and the European (ECMWF) model are moving this trough in a general westward direction after it forms. The GFS model keeps a more northwesterly track, which would result in advecting deeper tropical moisture into the islands for the first few days of next week. The latest GFS model run brings this deeper moisture and enhanced showers into the southern slopes of the Big Island late Sunday night or early Monday morning, this moisture pushes northward into East Maui by Monday afternoon. Isolated thunderstorms are also possible over the Big Island starting early Monday morning. Meanwhile the ECMWF weather model keeps us in a drier air mass for most of this time period, with the deeper tropical moisture passing just south of the state. The latest 00Z ECMWF is starting to trend more towards the GFS solution. We are keeping a close watch on these model differences and have trended the morning forecast grid package towards the wetter GFS solution for the Big Island and Maui starting early Monday morning through Tuesday. Some of this deeper moisture may move into the upstream trade wind flow for windward and mountain slopes across the western half of the state by Monday afternoon. Our confidence in these enhanced showers for the eastern half of the state remains fair at this time. More typical easterly trade wind weather returns from Wednesday onward with passing shower bands in the moderate to breezy easterly wind flow. && .AVIATION... Strong high pressure far northeast of the Main Hawaiian Islands will persist. Bands of weak trade wind showers will continue to impact mainly northeast through east facing slopes and coasts. AIRMET Sierra may become necessary for Windward portions of Kauai later this morning. Light to locally strong east winds will continue into Saturday and likely beyond. AIRMET TANGO will remain in effect for moderate turbulence below 7,000 ft. && .MARINE... Fresh to locally strong easterly trades are forecast to continue through next week as high pressure remains positioned north-northeast of the area. The stronger winds will remain across the typically windier locations from Maui County to the Big Island due to terrain accelerations. The current Small Craft Advisory remains in place for these areas through Sunday and may need to be extended into early next week. Rough surf will continue along east facing shores each day due to strong onshore winds. Heights are forecast to slightly trend down through the latter half of the weekend into early next week due to the upstream trades trending down. Surf along south facing shores will remain small through the weekend, then trend up through the first half of the upcoming week due to a recent system passing through/near the Tasman Sea. Heights should remain below advisory levels as this south- southwest swell moves through and peaks Monday through Tuesday. In addition to this long-period source, a combination of small south to southeast swells will be enough to keep the surf from going flat along southern exposures through midweek. A south-southeast (150-160 deg) long-period swell associated with a compact gale that has developed southeast of the Tuamotus will be possible late next week with a peak around Thursday night into Friday. Surf will rise along exposed shores but should remain below advisory levels. See the latest Oahu Surf Discussion (SRDHFO) for additional details on surf and swell. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Bohlin AVIATION...Bedal MARINE...Gibbs Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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