A breezy to windy trade wind pattern will gradually wane through the rest of the week. Moisture embedded in the trades will allow showers to favor windward and mauka areas. An overall wetter pattern is possible this weekend as additional moisture is drawn over the island chain.
At the surface, strong high pressure remains centered north- northeast of the islands, with a front located northwest of Kauai. Winds across the state are at or very near advisory levels which are sustained speeds of 30-39 mph and/or gusts 50-57 mph, especially over higher terrain, passes, and areas immediately south through west of mountains. Latest observations show that the strongest gusts have occurred over the typically windier locations of Molokai, Maui County and the Big Island, with Gales in the windier waters and channels surrounding Maui County and the Big Island.
A mid-level dry airmass will remain in place in support of a strong inversion. Gradient winds are expected to remain nearly unchanged as the surface high remains to our north and the front remains nearly stationary to our west. Based on this, the Wind Advisory has been extended in time through 6am HST Thursday. By Thursday afternoon, winds will begin to slowly decrease, but still remain locally strong throughout the rest of the week.
As far as precipitation is concerned, little change is expected over the next few days, with showers and clouds embedded within the trades favoring windward and mauka areas. Things begin to get a bit more interesting over the weekend, as an overall pattern shift may lead to few days of wet and unstable trades this weekend into early next week.
Latest guidance remains in good agreement that moist southeast flow in the lower levels could expand moisture over the islands this weekend, then stall it over the state into Sunday. This is being closely monitored for potential flooding that could develop in this scenario. Forecast confidence will largely depend on the expected strength of trades, which will in turn modulate forward motion of showers. Guidance indicates that the islands could reside somewhere along the gradient between stronger trades to the east and light southeast flow to the west (where exactly this sets up could make for a large difference in rainfall potential for the islands). Still too early for specifics and what impacts we will face. Please continue to monitor forecasts in the coming days as details begin to iron out.
Breezy to strong easterly trade winds are expected to ease slightly on Thursday as the strong high pressure to the north temporarily weakens. Mid level ridging will keep conditions stable, which could enhance the wind gusts, as well as keep showers relatively shallow and light. Showers will focus over mainly windward and mountain areas, and will likely be more widespread during the overnight hours. Conditions should stay mostly VFR with pockets of MVFR at night with any passing showers.
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 will likely continue through tonight.
Strong high pressure will remain far northeast of the state during the next couple of days, as a slow moving front approaches from the west. The front will stall out and weaken into a trough just a few hundred miles west of the islands this weekend, with a new high building in to the distant north. A Gale Warning has been extended for the Pailolo and Alenuihaha Channels through tonight, with a Small Craft Advisory (SCA) in effect for all other waters through Thursday afternoon. The trade winds and seas are then expected to gradually lower Friday through the weekend. Some unsettled weather is expected over the weekend as an upper level trough moves over the state. Isolated thunderstorms are expected over the offshore waters and may be possible over the coastal waters as well, especially windward waters.
Surf will hold relatively steady along east facing shores during the next couple of days, and as a result the High Surf Advisory (HSA) is in effect through Thursday afternoon. As the trade winds gradually ease Thursday into the weekend, surf along east facing shores will gradually lower below HSA thresholds.
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 Thursday for Olomana-Maui Windward West-Kauai East-Kauai South-East Honolulu-Koolau Windward-Molokai Windward-Molokai Southeast-Windward Haleakala- Kipahulu-Big Island Southeast-Big Island East-Big Island North.
Wind Advisory until 6 AM HST Thursday for Waianae Mountains- Lanai Mauka-Kahoolawe-Maui Windward West-Kohala-Big Island Interior-Koolau Leeward-Molokai Windward-Molokai Southeast- Molokai North-Molokai West-Lanai Windward-Lanai Leeward-Lanai South-Maui Central Valley North-Maui Central Valley South- Windward Haleakala-South Haleakala-Big Island South-Big Island Southeast-Big Island North.
Small Craft Advisory until 6 PM HST Thursday for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters-Kauai Channel- Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters-Maalaea Bay- Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters.
Gale Warning until 6 AM HST Thursday for Pailolo Channel- Alenuihaha Channel.
