Waihee-Waiehu, HI Weather

Synopsis

Gentle to moderate northeast trade winds expected for next few days. Deep tropical moisture will bring the potential for heavy rain and thunderstorms across the state starting late tonight through at least Thursday. The forecast for next weekend is a return of trades but continued above-normal rainfall.

Discussion

Currently (3AM HST), radar and satellite imagery shows a few scattered showers and clouds across the state. Expect northeasterly trades to gradually decrease today. As we head into this evening and for the next few days the weather pattern gets rather complicated.

A large vertically stacked low sits about 800 miles to our northeast. A front extends to the east and then south of the low, and a trough extends southwest from the decaying end of the front toward Hawaii. A separate upper level trough is our northwest and Tropical Storm Olana sits to our southwest. The northwestern trough will sag southeast helping pull Olana toward the islands. Tropical Storm Olana is expected to weaken into a tropical depression and stay to the west of the islands Tuesday. The trough extending from the low to our northeast will eventually extend all the way to the remnants of Olana, and then drift north over the state. This trough will bring abundant tropical moisture with PWATs close to 2.5 inches and remain nearly stationary over the area through the end of the week. A series of small lows will form with one or more potentially moving over the state. Models still show disagreement on timing and locations of these features. This makes the uncertainty higher than normal.

With the potential for heavy rain and a few thunderstorms continuing over the state for a few days a Flood Watch will go into effect at 6AM Tuesday through Wednesday evening with the potential of it being extended. Total rainfall amounts Tuesday through Thursday range from 2 to 8 inches, with the highest amounts in the higher elevations. There is also a chance of a few thunderstorms at times during this timeframe. With any thuderstorms brief gusty winds and very heavy rain can be expected. We look to return to a trade wind pattern this weekend into early next week.

Aviation

Gentle to moderate trades through the period. Low cigs and SHRA should impact windward and mauka locations. MVFR conds possible in heavier SHRA, otherwise VFR prevails. The next weather system arrives Tuesday through the rest of the week bringing heavier SHRA and TSTMs with IFR/MVFR conds.

No AIRMETs in effect.

Marine

A surface low far northeast of the Hawaiian Islands will stall roughly 800 nm northeast of the state today. A low pressure trough is forecast to approach the area by late tonight and bring heavy showers with embedded thunderstorms to the waters over the next several days. Relatively weak wind flow will persist through the forecast period.

A short period north northwest swell will gradually lower today. Meanwhile, an overlapping, moderate, mid- period northwest swell is will build today and bring surf to near advisory levels along north and west facing shores through Wednesday. A small north northeast swell should arrive during the second half of the week.

Overlapping south-southwest swells will keep surf along south-facing shores to around seasonal averages through Tuesday. A larger south swell may push surf up to near advisory levels Thursday and Friday.

Surf along most east-facing shores will be small through early this week, but areas exposed to wrapping northerly swells will experience periods of moderate surf today. East- facing shores should also see a bump in surf if the north- northeast swell materializes during the latter half of this week.