Breezy trade winds will persist through today, with showers favoring windward and mauka areas. An upper level disturbance will briefly move over the state on Friday and will bring the threat of heavy rain and isolated thunderstorms over select areas. While widespread heavy rain is not expected, pockets of heavy rain with some flooding impacts will be possible on Friday. Wetter than normal conditions will likely persist through the weekend especially over windward and mauka areas, where scattered showers are expected.
Broad high pressure far north of the state will maintain breezy trade winds across the region through today, delivering clouds and scattered showers to windward and mauka areas, particularly during the overnight to early morning hours.
Starting tonight, the weather pattern will begin to change as a cold upper level low drops southward towards the state. Latest global guidance are in good agreement with the upper level low centered over Kauai by Friday with 500 mb temps as cold as -14C. The strength of the upper level low should induce a surface trough, which should help act as a trigger for heavy showers and isolated thunderstorms on Friday. With the center of the upper low expected to be over Kauai, the best atmospheric forcing will be over Oahu and parts of Maui County where guidance is showing over 1000 J/kg of CAPE by Friday afternoon. While widespread heavy rain is not expected, we should see areas of heavy rain and with light winds in the lower levels of the atmosphere, any heavy rain that develops will be slow moving. With surface winds generally out of the east to southeast, combine that with a cold upper level low centered west of Oahu, generally is a favorable pattern for heavy rain to potentially anchor along the Koolau Mountain Range. While the threat for heavy rain will exist across the state on Friday, the highest confidence is currently over Oahu and portions of Maui County. A Flood Watch may be eventually needed for portions of the state and we will continue to watch how the upper level low evolves over the next 24 hours.
Over the weekend, the upper level low will begin to drift further away from the state, which should decrease the threat of thunderstorms. While the instability decreases over the weekend, low level moisture will increase from the southeast with precipitable water values approaching 2 inches by late Saturday over windward Big Island. Periods of heavy rain is expected over windward and southeast Big Island this weekend with some enhanced showers possible elsewhere across the state.
Breezy trades expected for next few days. Low cigs and SHRA expected along windward and mauka locations. MVFR conds possible but VFR should prevail.
AIRMET Tango is in effect for turb, lee of terrain due to the breezy trades.
High pressure established north of the islands maintains locally strong trades until an upper disturbance causes winds to weaken by this weekend. Our current fresh to locally strong trades should hold through the day today then gradually weaken and veer towards the east-southeast tonight into Friday. Moderate to fresh east to east-southeast winds are expected Friday into the weekend. The SCA remains in effect for the windier zones of Maui County and the Big Island through this afternoon. The upper level disturbance will bring the threat of heavy rain and isolated thunderstorms on Friday.
A new small to moderate, long period NW to NNW (320 degree to 330 degree) swell will steadily fill in this morning and will likely peak later today and produce above average surf along north facing shores. Latest readings on buoy 51001 did show swell heights of 4 feet 15 seconds, which is in line with guidance. This swell should gradually fade tonight into the weekend.
Small, medium to long period S swell maintains small surf along S shores. A series of gales initially passing south of New Zealand a few days ago and now setting up E of New Zealand should send a series of small south swells all of next week. Surf should rise to near the summer average around Sunday and hold near the summer average throughout next week. Meanwhile along east facing shores, locally strong trades will maintain rough and choppy surf along E facing shores. A slight decrease of wind swell is expected Thursday into Friday as the trades weaken to moderate to locally fresh speeds.
Tides peak around 2.5 ft MLLW this weekend. Combined with ongoing trades and a modest boost in S swell, water levels will peak around 3.0 ft late this weekend into early next week. Minor overwash of low lying coastal areas will be possible during the afternoon high tides at this time.
Small Craft Advisory until 6 PM HST this evening for Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters- Maalaea Bay-Pailolo Channel.
