Locally strong trades will gradually ease through the rest of the week. Moisture embedded in the trades will allow showers to favor windward and mauka areas through Friday. An overall wetter pattern is expected this weekend as additional moisture is drawn over the island chain.
Early this morning, regional infrared satellite imagery shows a line of strong thunderstorms along and ahead of a nearly stationary front west of the main Hawaiian Islands. This line of thunderstorms has been making its way eastward throughout the night, and is now near the western-most edge of the offshore waters area. High clouds ahead of these storms have begun moving into the western portions of the state this morning, and model guidance and satellite trends suggest increasing coverage of high clouds throughout the rest of the day.
Meanwhile, surface observations show that breezy trade winds are continuing to prevail across the islands, particularly across the typical wind-prone areas of Maui County and the Big Island, as strong high pressure remains centered far north of the state. With that said, winds have largely decreased to slightly below advisory levels, and are expected to continue a gradual decline throughout the day today as the high to our north weakens. Therefore, the Wind Advisory that was previously in effect for portions of Oahu through the Big Island has been cancelled with this morning's forecast updates. As far as precipitation is concerned, showers will continue to favor windward and mauka areas for the next couple of days, with showers and areas of low clouds embedded within the trades.
A more dynamic weather pattern looks to develop across the islands from Friday into the weekend, when the state could reside somewhere along the gradient between trades to the east and light southeast flow to the west. Model guidance has been fairly consistent in showing that southeast flow in the lower levels could expand moisture over the islands as early as Friday, then stall it over the state through the weekend. With 500mb temperatures cooling into the -10C to -13C range, and at least some instability in the region, felt it was worth adding isolated thunderstorms into the forecast with this morning's forecast updates, first for Kauai and then expanding eastward Friday into Sunday. It remains to be seen exactly how much instability will set up over the islands, however, as models are only showing surface dewpoints in the mid 60s or so. Regardless, the weekend looks to be a wetter pattern where localized flooding and isolated thunderstorms cannot be ruled out, particularly for windward areas. Winds will be lighter throughout this period, with locally strong trades forecast to return to the islands early next week.
Breezy trade winds are expected to ease slightly during the day today as strong high pressure to the north temporarily weakens. High clouds will move in as a result of a slow-moving low pressure system to our west, however shower activity is expected to remain isolated to windward sites through the period.
AIRMET Tango is in effect for tempo moderate turbulence below 8000 feet over leeward sides of the islands as a result of the strong low level winds. This AIRMET is expected to continue through the day today, however conditions may become marginal as winds decrease.
A strong high pressure system to the north and a low pressure system and front just west of the offshore waters will allow strong to near gale force east to east southeast winds to blow through Friday. Winds are expected to decrease gradually as the high pressure and front weaken, and then a new high builds in to the distant north by the weekend. A Small Craft Advisory (SCA) is in effect for all coastal waters through this afternoon due to a combination of winds and seas. This SCA will likely be modified and extended later tonight to include the typical windy areas as the winds decrease. The trade winds and seas are then expected to gradually lower Friday through the weekend.
Unsettled weather is expected Friday through the weekend as a mid and upper level trough is forecast to move over the islands from west to east. Isolated thunderstorms can be expected around Kauai and Oahu waters by Friday afternoon, then spread to the rest of the islands by the weekend. Windward waters currently appear to have the highest chance of thunderstorms. Winds look to be lighter to the south of each island, and fresh to the north of each island on Friday. Winds then become light and variable Saturday through Sunday.
Surf will hold relatively steady along east facing shores through today before gradually decreasing tonight through the weekend as winds decrease. The High Surf Advisory (HSA) is in effect through this afternoon.
Surf along north and west facing shores will remain well below seasonal levels through the weekend, and surf along south facing shores will remain small.
Forerunners from a large, long-period north to north-northeast swell are forecast to arrive Sunday night, then rapidly build to near warning levels along north facing shores Monday through Tuesday. Also due to the northerly direction, elevated surf heights are expected along west Maui and west Big Island near Kua Bay. Surf heights are expected to reach advisory threshold for west Big Island on Monday and could reach advisory threshold for west Maui as well. Lastly, due to the large swell and northerly direction (010-030 degrees), heavy surges are expected along north facing harbors such as Kahului and Hilo harbors.
High Surf Advisory until 6 PM HST this evening for east facing shores of Kauai, Oahu, Molokai, Maui, and the Big Island.
Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters-
