Moderate to locally breezy trades will persist through Thursday, focusing showers over windward and mauka areas while high clouds continue to stream overhead. Winds will weaken Thursday into Friday as a front approaches from the northwest, allowing for sea breeze development and limited shower activity over leeward and interior areas. Confidence remains lower in the weekend forecast, but the front is expected to bring breezy to windy northeasterly winds and increased showers to at least the western end of the state, with moisture potentially spreading farther east into early next week.
Current radar and satellite imagery show high clouds streaming northeast over the islands, with low clouds and isolated showers riding on the moderate trades to windward and mauka areas. These upper- level clouds will continue drifting overhead for the next couple of days which should have minimal impact on the weather besides perhaps helping to moderate temperatures a bit, but should make for some dynamic sunrises and sunsets.
As the tail-end of a cold front to the north of the state transitions into a surface trough by Wednesday evening, the high pressure to our northwest and another high pressure center building to the distant northeast will help to drive moderate to locally breezy trade winds across the region through Thursday. At the same time, a mid level ridge will build over the state, maintaining a fairly stable tradewind pattern into Thursday, focusing shallow clouds and showers mainly across windward and mauka areas. In addition, leeward areas of the Big Island will see sea breeze activity with the typical afternoon showers.
Winds begin to weaken on Thursday as a cold front approaches the region from the northwest, with lighter veered winds over the western end of the state allowing for localized sea breeze activity over Kauai and Oahu. With limited low level moisture being brought in on the weakening trades at that time, these sea breezes will likely only bring some clouds and perhaps a few isolated showers to leeward and interior areas Thursday afternoon.
The trades are expected to fully collapse by Friday, giving way to light and variable or northerly winds as the front nears Kauai. While moisture still looks to remain somewhat limited, statewide sea breeze activity will build low level clouds over leeward and interior areas and once again likely only produce isolated shower activity.
Forecast confidence decreases heading into the weekend due to model differences in the position and timing of the approaching front. Confidence is higher that the front will at least reach the western islands, where breezy to windy northeasterly winds and increased showers are expected. Ensemble guidance shows some members stall the front near Kauai, others across the central islands, and a few progress it all the way down to the Big Island, hence the decreased confidence.
The weather early next week will be dependent on the evolution of the aforementioned front. It looks like most of the state will see breezy to windy NE trades with enhanced moisture near the frontal boundary. With mid level ridging building back over the region, inversion heights will lower once again, keeping the moisture confined to lower levels and focusing clouds and showers over windward and mauka areas.
Moderate to locally breezy trades continue to persist across the state for the next few days under a broad upper-level high situated north of the islands. Expect brief periods of MVFR conditions across the Big Island, namely PHKO and PHTO, for low clouds and isolated shower activity. Otherwise, VFR conditions prevail.
AIRMET SIERRA remains in effect for mountain obscuration across windward Big Island through 1600z and may be continued through mid morning.
A high pressure ridge north of the Hawaiian Islands will build today, increasing the trade winds into the fresh to locally strong range today into tonight. Winds then decrease from Thursday onward as a cold front approaches the region from the northwest. A large medium period north-northwest swell will build into the region today. These stronger winds and higher seas will produce Small Craft Advisory (SCA) conditions for most coastal waters into Thursday. The current SCA was expanded to include windward Oahu and Kauai waters for seas, and extended in time through Thursday. Trade winds will gradually decline from Thursday through Friday as a cold front north of the Islands moves into the region from the north. Global models show this cold front weakening and stalling over the northwestern and central waters from Saturday to Sunday. Stronger northeast winds will blow across waters north of the front, with moderate easterly winds south of the frontal boundary.
A gale force low that passed far north of the state on Monday has produced a moderate to large medium period north-northwest (340-350 degree) swell that will build into Hawaiian waters through Thursday. Surf heights along exposed north and west facing shores will exceed surf advisory thresholds into Thursday, before steady declining. A High Surf Advisory (HSA) was issued this morning for these areas. An overlapping north-northwest swell will move into the region by Friday, helping to maintain moderate surf heights along north and west facing shores. In the longer range forecast, a deep low pressure system is expected to develop to our north and northeast from Friday into Saturday. This low will likely generate a large north-northeast (020-030 degree) swell late this weekend, easily exceeding HSA thresholds. Due to the swell angle, heavy surges will be possible along north facing harbors such as Kahului and Hilo on Sunday.
South facing shores will remain small throughout this week. A small long-period south-southwest swell will boost south shore surf heights from Thursday into the weekend, along with a larger out of season south swell possible by early next week. Surf for east facing shores should be rough and choppy tomorrow with the increasing trade winds and could also see a little bit of north wrap from the medium period north-northwest swell.
Peak monthly tides combined with water levels that are running higher than predicted will lead to minor flooding along the shoreline and in low-lying coastal areas. The greatest chance for coastal flooding will occur during the daily peak high tide during the early morning hours, and along north facing shores exposed to the large north-northwest swell.
High Surf Advisory until 6 PM HST Thursday for Kauai Leeward- Waianae Coast-Oahu North Shore-Maui Windward West-Kauai North- Molokai Windward-Molokai North-Molokai West-Maui Central Valley North-Windward Haleakala-Big Island East-Big Island North.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters-Kauai Windward Waters-Oahu Windward Waters- Kaiwi Channel.
Small Craft Advisory until 6 AM HST Thursday for Maui County Windward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel- Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters.
