| Current Conditions | ||
| Temp |  | 6.5 C |
| RH | | 66 % |
| Wind | | SW 24 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 951 FXHW60 PHFO 201933 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 933 AM HST Wed Sep 20 2017 .SYNOPSIS... Moderate to locally strong trades will continue through the work week, thanks to persistent high pressure to our north. Wind speeds will decrease slightly beginning this weekend as the main high drifts eastward. Clouds and showers will favor windward and mauka areas, mainly at night and during the morning hours. && .DISCUSSION... A 1032 mb high far north of the main Hawaiian Islands continues to drive moderate to strong trade winds across local waters this morning. An area of broken low clouds embedded within this trade flow lies across the island chain, with radar showing associated moderate showers across windward portions of Kauai, Oahu, Molokai Maui and the Big Island. We expect cloud and shower coverage will decrease a bit this by afternoon as the cloud area mixes out and slides west of us. Water vapor loop shows an upper low about 800 miles northeast of the islands. While this feature may have raised inversion heights and allowed shower-bearing clouds to build a bit taller recently, overnight soundings also show a stable airmass and only 1.2 to 1.5 inches of PW. Models show the upper low and associated upper trough will deepen and dig southward over the next few days, but remain northeast and east of the the island chain. In short, at this time we expect only minimal shower enhancement from this upper trough through the forecast period. Models show the high to our north drifting eastward and weakening over the next few days. The trailing ridge will be pushed closer to the islands by a cold front, but the front itself will not reach us. Weaker high pressure will cause trade winds to decrease a bit across local waters by this weekend. However, with no disruptions from intervening surface troughs or fronts forecast into next week, we expect continued trade flow and a trade wind weather distributions of clouds and showers to continue through the forecast period. Total rainfall will be light. && .AVIATION... Moderate to locally breezy trade winds will continue today, with clouds and showers favoring the windward and mountain areas. AIRMET SIERRA for mountain obscuration is posted for the north through east sections on the Big Island this morning. Conditions should improve over the next few hours. Otherwise, expected predominately VFR conditions. AIRMET TANGO is posted for low level turbulence over and immediately south through west of the mountains. && .MARINE... A ridge of high pressure far north of the state remains in place and is strong enough to keep trade winds above Small Craft Advisory (SCA) criteria in the Pailolo and Alenuihaha Channels, Maalaea Bay, and the waters south of the Big Island. The ridge is forecast to weaken slowly over the next several days which will allow conditions to drop below SCA levels. An approaching cold front far to the northwest will push the ridge toward the state over the weekend and further weaken the trades. The persistent moderate to fresh trade winds over and upwind from the main Hawaiian Islands will continue to produce rough surf along the east-facing shores through Friday. As the trades diminish during the weekend, surf along the east-facing shores will trend down. For the north- and west-facing shores, a small northwest swell is expected to arrive on Thursday and persist through Saturday. South-facing shores should just see small background surf from the southeast and south-southwest directions through the weekend. && .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...Powell AVIATION...Eaton MARINE...Kodama Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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