Dry, stable, breezy trades will continue through today, bringing limited showers mainly along windward and mauka areas. Winds will begin to ease later today through Tuesday. A developing area of low pressure north of the state will further weaken winds and turn them out of the south Wednesday. Chances of showers will increase during the second half of the week as well as the potential for heavy rain across Hawaii.
Latest surface analysis shows high pressure north of the state and a weak disturbance passing to the south, resulting in breezy trade winds. Radar and satellite imagery show scattered low clouds with embedded light showers. Overnight rainfall totals range from .20 to .30 inches of rainfall mostly for windward and mauka areas of Maui County and the Big Island. Modest amounts were observed over the the rest of the state as shower coverage becomes more isolated. Chances of showers will trend down through the day today. Winds will gradually ease later today and tonight as the high north of the state weakens and shifts northeast. Showers will remain limited along windward and mauka areas.
A hybrid land/seabreeze and light trade wind pattern will develop Tuesday as winds continue to ease. Winds will then veer southeasterly by late Tuesday, and south by Wednesday, as a sharp trough approaches from the northwest. A surface low will form along the trough and southerly winds will draw deep tropical moisture over the islands, while a cold pool aloft associated with the upper low will act to destabilize the atmosphere over the state. PW values will increase to around 2 inches and dewpoints will rise to around 70 Thursday and into the lower 70s Friday. As this deeper moisture moves in with increasing instability, heavy rain will become likely. The timing and location of the moisture continues to be depicted slightly different in the long range models, but at this time it appears all the islands will be impacted at some point. Thus, not getting too specific in the forecast details for now, but expect an overall wetter pattern and southerly winds from around late Wednesday through at least Friday, and possibly lingering into the upcoming weekend.
Moderate to breezy trade winds will continue across the region today with isolated showers favoring windward and mountain areas where short-lived MVFR conditions are possible. Otherwise, VFR conditions will prevail across the state.
AIRMET Sierra remains in effect for mountain obscuration across much of the Big Island early this morning. Improving conditions are expected later today.
AIRMET Tango also remains in effect for moderate turbulence downwind of mountain terrain due to the breezy trades.
High pressure north of the Hawaiian Islands will maintain fresh to locally strong trade winds today. The Small Craft Advisory for the windier waters and channels around Maui County and the Big Island remains in effect through this afternoon. Thereafter, high pressure to the north weakens and trades will start to diminish. Troughing developing northwest of the islands will likely cause winds to veer out of the southeast around midweek and bring increased shower activity for the latter half of the week.
A new small, long-period south swell will slowly fill in today and tonight, causing surf along south and west facing shores to increase to slightly above seasonal averages Tuesday into Wednesday. Surf is then forecast to drop to near or slightly below average for the rest of the week, maintained by a mix of new, small south swells.
A small, medium-period northwest swell builds this morning and peaks late today, producing a small bump in surf along north-facing shores that begins fading on Tuesday. However, a larger, long-period northwest swell will arrive on Tuesday that will push surf higher into Wednesday. Surf is then likely to hold through the end of the week even as swell energy becomes shorter period as it is reinforced by a low to the north-northwest of the Hawaiian Islands. Surf along east facing shores will fall below seasonal averages as locally strong trades diminish tonight.
A small, long-period west swell originating from Typhoon Choi-wan is forecast to reach the islands Thursday into the weekend, which may produce moderate surf for west-facing shores of the Big Island.
Small Craft Advisory until 6 PM HST this evening for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.
