Breezy trades expected through the middle of next week. An upper level trough and moisture associated with the remnants of Norbert will fill in across the state from east to west Thursday into Friday, increasing the chances of heavy rain, isolated thunderstorms, and flash flooding, especially for the windward and mauka areas. Drier air will move back in this weekend behind the departing trough. Moisture from the remnants of Tropical Depression 15-E may bring another round of enhanced trade showers around next Tuesday and Wednesday.
Afternoon satellite imagery shows an upper level low around 1400 mi north- northeast of the islands with a trough extending southwestward. Isolated light showers continue to move westward with the greatest coverage from Maui northward. Trade winds will continue to strengthen through the afternoon as the upper trough approaches.
The upper level trough will dig southwest tonight into Thursday, pulling in remnant moisture from Norbert. Satellite imagery shows a broad area of precipitable water in excess of 2" beginning to move into the Big Island, and is forecast to move across the remaining islands tonight into Thursday. Deeper moisture and increasing instability will bring moderate to locally heavy showers and a slight chance of thunderstorms, with the highest threat of thunderstorms across the Big Island Thursday afternoon. Heaviest rain is expected on the windward and mauka areas. With soil moisture likely still high from previous heavy rain events, there is an increased risk of flash flooding where heavier showers and thunderstorms occur.
Moisture will decrease from east to west late Friday through the weekend. There is the potential for another round of increasing moisture from the remnants of tropical depression 15-E moving into around Tuesday to Wednesday of next week. Ensembles show at least a weak low-level wave associated with this moisture, though further aloft only 6% of the ensemble members have some form of troughing while the remainder keep us under a ridge, limiting the potential for heavier showers.
Moderate to locally breezy trade winds will strengthen to breezy levels this afternoon and a trough will approach the area from the east. Showers and low clouds associated with that trough will increase with the trade wind flow from east to west starting early tonight for the eastern half of the state, then spread west late tonight into tomorrow morning. More widespread MVFR conditions will be possible as the moisture associated with the trough moves in, especially for windward and mountain areas.
No AIRMETs are currently in effect. There is the possibility for AIRMET Tango during the afternoon once trade winds strengthen. There is also potential for AIRMET SIERRA later today as clouds increase on the windward slopes.
A broad trough, associated with the remnants of Tropical Storm Norbert, will approach the state from the east tonight, allowing moderate to locally strong northeast trades to hold through tonight. This afternoon ASCAT pass showed borderline Small Craft Advisory (SCA) conditions around Maui County and the Big Island leading to less confidence that SCA conditions will hold as the trough passes over the state Thursday, thus have not extended the SCA at this time. After the trough moves through the state Thursday into Friday, a surface high far northeast of the state could allow moderate to locally strong trades to return over the weekend through the forecast period. Above normal moisture and upper level support will allow isolated thunderstorms with localized heavy rain and gusty outflows to develop over the offshore waters tonight through Saturday.
A series of long to medium period south-southwest to south swells will continue fill tonight. Surf along south facing shores should begin to see more consistent sets tonight into Thursday as build to near average. A reinforcing southerly swell will fill in Friday bumping surf near High Surf Advisory thresholds by this weekend as swells shift more out of a south direction.
Surf along east- facing shores increases today into Thursday as trade winds strengthen and a small, medium- period east swell from the remnants of Norbert arrives. Flat to tiny surf along north facing shores is expected through the forecast period.
Flood Watch through late Thursday night for Big Island East-Big Island Interior-Big Island North-Big Island South-Big Island Southeast-Big Island Summits-Central Oahu-East Honolulu-Ewa Plain-Haleakala Summit-Honolulu Metro-Kahoolawe-Kauai East-Kauai Mountains-Kauai North-Kauai South-Kauai Southwest-Kipahulu- Kohala-Kona-Koolau Leeward-Koolau Windward-Lanai Leeward-Lanai Mauka-Lanai South-Lanai Windward-Maui Central Valley North-Maui Central Valley South-Maui Leeward West-Maui Windward West- Molokai Leeward South-Molokai North-Molokai Southeast-Molokai West-Molokai Windward-Niihau-Oahu North Shore-Olomana-South Haleakala-South Maui/Upcountry-Waianae Coast-Waianae Mountains- Windward Haleakala.
Small Craft Advisory until 6 AM HST Thursday for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.
