Hilo

Today: Showers and slight chance of thunderstorms until late afternoon, then showers likely and slight chance of thunderstorms late in the afternoon. Locally heavy rainfall possible until late afternoon. Highs 76 to 81 near the shore to around 68 at 4000 feet. Northwest winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Showers likely and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows around 70 near the shore to around 56 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 78 to 84 near the shore to 67 to 72 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Kona

Today: Mostly cloudy. Isolated showers until late afternoon. Slight chance of thunderstorms in the afternoon. Scattered showers late in the afternoon. Locally heavy rainfall possible late in the afternoon. Highs around 81 near the shore to around 71 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the evening, then isolated showers in the late evening and overnight. Lows 70 to 75 near the shore to around 56 near 5000 feet. Light winds. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Isolated showers in the afternoon. Highs around 84 near the shore to around 72 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Waimea

Today: Breezy. Showers and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs 66 to 81. East winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows around 69 near the shore to 56 to 63 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 80 near the shore to 72 to 79 near 3000 feet. East winds 10 to 25 mph. Gusts up to 45 mph in the afternoon. Chance of rain 40 percent.

Kohala

Today: Breezy. Showers and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs 66 to 81. East winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows around 69 near the shore to 56 to 63 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 80 near the shore to 72 to 79 near 3000 feet. East winds 10 to 25 mph. Gusts up to 45 mph in the afternoon. Chance of rain 40 percent.

South Big Island

Today: Breezy. Cloudy with isolated showers and slight chance of thunderstorms. Highs around 81 near the shore to around 72 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with slight chance of thunderstorms and isolated showers early in the evening, then partly cloudy in the late evening and overnight. Lows around 70 near the shore to around 55 near 5000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly cloudy. Breezy. Highs around 84 near the shore to around 73 near 5000 feet. East winds up to 20 mph.

Puna

Today: Showers and slight chance of thunderstorms until late afternoon, then showers likely and slight chance of thunderstorms late in the afternoon. Locally heavy rainfall possible until late afternoon. Highs 76 to 81 near the shore to around 68 at 4000 feet. Northwest winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Showers likely and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows around 70 near the shore to around 56 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 78 to 84 near the shore to 67 to 72 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Waikoloa

Today: Mostly cloudy. Isolated showers and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible late in the afternoon. Highs around 81 near the shore to 67 to 73 above 4000 feet. East winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers and slight chance of thunderstorms early in the evening, then scattered showers in the late evening and overnight. Lows around 73 near the shore to 52 to 59 above 4000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Wednesday: Mostly cloudy. Breezy. Highs around 83 near the shore to 68 to 74 above 4000 feet. Northeast winds up to 20 mph. Gusts up to 45 mph in the afternoon.

Detailed Forecast

Synopsis

Strong trades will bring widespread windward showers tonight into Tuesday, especially over Big Island and Maui where there is a the potential for locally heavy rainfall through Tuesday. Trades will gradually trend toward moderate by this weekend as the surface high weakens far northeast of the islands.

Discussion

Strong but weakening surface high pressure far to the northeast of the islands means that the trade winds will continue to trend softer in the coming days. The process will be slow but gradual, so perhaps by Thursday night, locally strong trades will be confined to Maui and Hawaii counties. Currently, moderate to strong trades cover all islands. Further weakening of the trades to moderate speed may come over the weekend.
A wet and active forecast lies ahead for tonight and Tuesday as a large area of low clouds spreads westward. But it is Maui and the Big Island where we will be watching closely as deeper moisture is slated to move into the windward sections of these two islands in the coming hours. This moisture will be aided by not only terrain effects but an upper level disturbance that will further enhance this moisture, leading to locally heavy rainfall tonight and Tuesday. The detection of lightning from deep convection over the waters east of the Big Island this afternoon, prompted the inclusion of a slight chance of a thunderstorm for these two islands into the forecast for the tonight period. The models agree that the strongest dynamics favoring thunderstorms is to occur tonight.
Locally heavy showers with rainfall rates of up to one and one half inches an hour are occurring along the Hamakua coast and down into the Mountain View area of the Big Island, prompting in a Flood Advisory. We are looking at 2 to 4 inches in the wetter upslope areas of Big Island and Maui with locally higher amounts of 5 inches possible, especially if any thunderstorms develop over the windward slopes. So far elsewhere around the main Hawaiian Islands, is passing showers, favoring the windward and mountain areas.
This moisture is slated to begin diminishing Tuesday afternoon area wide, while upper ridging starts to build across the area. Look for a more typical trade wind weather pattern with lighter rainfall will return by sunrise Wednesday.

Aviation

Trade winds will remain breezy to locally strong through Tuesday, and beyond, as robust high pressure remains entrenched far to the north and northeast. An upper level disturbance northeast of the islands is enhancing showers, and thus MVFR conditions, around the area, and also may ignite a thunderstorm or two over the eastern part of the island chain.
An AIRMET continues in effect for low level turbulence to the lee of the mountains over all islands. Other AIRMETs have been issued for TEMPO mountain obscuration in windward sections of each isle.

Marine

Hazardous marine conditions will continue through midweek due to strong trade winds and large seas ranging from 8 to 12 feet (mostly short period/wind-driven seas). The Small Craft Advisory will possibly need to be extended for all waters through Wednesday. Although a gradual downward trend (winds/seas) is anticipated Thursday through the weekend, advisory-level winds will remain possible for the windier waters/channels around Maui and the Big Island through Friday. In addition to the winds and seas, locally heavy showers and a few storms associated with an upper disturbance nearby and increasing moisture will be possible through Tuesday – best chances being across the Big Island and Maui County waters.
Surf along east facing shores will remain rough through the week due to the aforementioned winds and seas. A gradual downward trend, however, is expected through the second half of the week and upcoming weekend as the gradient far upstream of the state and the local winds weaken.
Surf along south facing shores will slowly ease through Thursday as the south swell that peaked over the weekend moves out. Observations at the offshore buoys to the south this evening reflect a solid amount of energy holding in the 14-16 second bands. A return to small surf is expected Friday through the weekend with no significant southerly energy anticipated.
Surf along north facing shores will remain small through midweek. The exception will be at north facing locations exposed to the trade wind energy, which will result in rough conditions. Guidance does show a gale racing eastward across the Kamchatka Peninsula and southern Bering Sea through Tuesday with a short-lived fetch setting up within the 315 to 330 directional band relative to Hawaii. WAVEWATCH III reflects this and depicts a small, long- period northwest swell arriving Thursday night into Friday.
Looking ahead into next week (lower confidence), guidance suggests a significant gale- to storm-force low racing eastward over the Aleutians this weekend, then southeastward into the Gulf of Alaska early next week. As this feature turns southeastward, a large area of gale /storm-force winds become focused at the islands around the 350 directional band driving seas to around 30 ft. GFS- Wave and ECMWF-Wave solutions reflect this and depict a solid northerly swell arriving in the islands late Tuesday through midweek. If this materializes, surf could exceed the advisory level for north facing shores come next Wednesday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Tuesday for Olomana, Kauai East, Kauai South, East Honolulu, Koolau Windward, Koolau Leeward, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, South Haleakala, Big Island Southeast, Big Island East, Big Island North.
Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian waters,

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Data Courtesy of NOAA.gov