Moderate to locally breezy trades will persist tonight into Thursday, focusing brief 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 visible satellite imagery show a plethora of high clouds streaming northeast over the islands, with low clouds and isolated showers moving into windward and mauka areas on the moderate trades. These upper-level clouds, tied to jet dynamics aloft, 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 tonight into Thursday. During this time, a mid level ridge will build over the state, increasing stability and keeping inversion heights on the lower side, maintaining a fairly typical 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 remains split, 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.
The weather early next week will be highly dependent on the evolution of the front. For now, it’s looking 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 trade winds will persist for the next couple of days as high pressure sits north of Hawaii. A low pressure system to the west will draw high clouds northeastward across the state into Wednesday.
Low clouds and showers are forecast to move onto windward Maui and Big Island soon. AIRMET Sierra for tempo mountain obscurations above 2500 feet will go into effect for windward Big Island at 03Z, and windward Maui by this evening.
A ridge of high pressure will strengthen north of the Hawaiian Islands through tomorrow, and cause the trade wind speeds to slightly increase to locally strong from tonight into Wednesday. As a result, a Small Craft Advisory (SCA) will be in effect for tonight and tomorrow. Trade winds are then forecast to gradually decline Thursday through Friday as a cold front north of the Islands moves towards the area and weakens the ridge. Global models then indicate the cold front could move over part or all of the islands at some point this weekend and bring locally fresh north northeasterly winds. Confidence on this is low due to model disagreements, but will become more clear in the next few days.
Surf heights will fall this evening as a short to medium period north swell decreases before a moderate to large swell arrives late tonight into tomorrow morning. Winds will ramp up later tonight and Small Craft Advisory criteria will be effect as a result, where a combination of winds and seas will likely produce SCA conditions in most coastal waters and channel areas.
A gale low currently passing far north of the state will send the next moderate to large medium period north-northwest swell later tonight and peak late Wednesday. Surf heights should exceed advisory thresholds along exposed north and west facing shores and hold into Thursday, before steadily declining. A High Surf Advisory (HSA) is expected to be issued tonight once the outer buoys confirm the size of swell, given the fact that model guidance has not been as reliable from past swells. A reinforcing north-northwest swell is possible on Friday, which should help maintain moderate surf. In the long range, a deep low pressure system is expected to develop to our north and northeast Friday into Saturday. If this low forms as predicted, it will likely send a large north-northeast (020-030 degree) swell late this weekend. 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 is possible Friday into the weekend 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 N wrap from the 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, which will be during the early morning hours.
Small Craft Advisory from 8 PM this evening to 6 PM HST Wednesday for Maui County Windward Waters-Maalaea Bay-Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters-Big Island Leeward Waters-Big Island Southeast Waters.
