| Current Conditions | ||
| Temp |  | 5.0 C |
| RH | | 61 % |
| Wind | | NE 15 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 136 FXHW60 PHFO 221955 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 955 AM HST Tue Aug 22 2017 .SYNOPSIS... An upper level low northwest of the islands will continue to bring the chance for locally heavy showers, and the slight chance of thunderstorms today. Otherwise, building trade winds will focus clouds and showers over the windward areas. Breezy trade winds and drier conditions will return Wednesday and continue into the upcoming weekend as high pressure strengthens north of the state. Trade winds are forecast to relax by the end of the upcoming weekend as high pressure weakens to the north. && .DISCUSSION... An upper level low is about 275 miles northwest of Kauai this morning based on water vapor imagery. This upper level feature has helped to destabilize the atmosphere over the region over the last few days. The low is forecast to continue to move to the west/west northwest over the next couple of days. Its influence on our local weather should diminish over the next 12 to 24 hours as it moves away from the area. During the pre-dawn hours, there was a thunderstorm just south of Niihau. Due to the proximity to the upper level low, thunderstorms remain a possibility near Kauai and Niihau today. Build-ups on the Big Island will also be possible, mainly during the afternoon hours. Across the state, building trade winds will focus clouds and showers over windward areas, but the instability provided by the nearby upper level low could mean heavier showers at times today. A surface high building far north of the islands will maintain the trade wind flow into the weekend. Moderate to locally breezy trades are expected, so while most shower activity will be focused over the windward and mauka areas, don't be surprised if a few showers reach leeward areas. Winds will likely drop a touch over the weekend as the high begins to weaken. && .AVIATION... Over the next 24 hours, a surface high will build far N of the area, while a low aloft NW of Kauai moves W. This will lead to strengthening trade winds and a reduction in shower coverage and intensity. In the meantime, the island atmosphere remains sufficiently unstable to support the development of +SHRA/+TSRA which have the potential to bring IFR CIG/VIS. Most likely location for MVFR/IFR conditions in the short term is over and near the Big Island and windward Maui, where AIRMET SIERRA remains in effect for mountain obscuration. The increasing winds have also prompted the issuance of AIRMET TANGO for low- level turbulence. && .MARINE... With trade winds on the increase, a Small Craft Advisory (SCA) is currently in effect for the typically windier zones around Maui County and the Big Island. The SCA is in effect through Thursday afternoon. An upper level low has been heading west away from the islands, but will still likely produce isolated thunderstorms over coastal and offshore waters through the day. The highest risk is for the waters in the west half of the forecast area. More stable and drier conditions are expected Wednesday and through the second half of the week. East-facing shores should see a slight increase in surf heights as the trade winds rebuild today. A longer period east swell may also arrive during the second half of the week as a result of tropical cyclone activity in the eastern Pacific. South-facing shores may see a slight increase in surf this weekend from a swell train that originated from a Tasman Sea gale. A small background southeast swell is also expected through the forecast period. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Thursday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...M Ballard AVIATION...Birchard MARINE...Kinel Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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