Hilo

Rest Of Tonight: Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 65 to 72 near the shore to 57 to 63 at 4000 feet. Southeast winds up to 10 mph. Chance of rain near 100 percent.

Tuesday: Occasional showers and slight chance of thunderstorms in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 78 to 84 near the shore to around 66 at 4000 feet. East winds up to 10 mph. Chance of rain near 100 percent.

Tuesday Night: Occasional showers. Lows 63 to 70 near the shore to 53 to 59 at 4000 feet. Northeast winds around 10 mph. Chance of rain near 100 percent.

Kona

Rest Of Tonight: Cloudy with occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 76 near the shore to 52 to 57 near 5000 feet. Light winds. Chance of rain 80 percent.

Tuesday: Mostly cloudy with scattered showers. Highs 83 to 88 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows around 73 near the shore to 48 to 54 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Rest Of Tonight: Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 66 to 73 near the shore to 58 to 65 near 3000 feet. Southeast winds up to 10 mph. Chance of rain near 100 percent.

Tuesday: Occasional showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 65 to 84. East winds up to 15 mph. Chance of rain near 100 percent.

Tuesday Night: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Kohala

Rest Of Tonight: Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 66 to 73 near the shore to 58 to 65 near 3000 feet. Southeast winds up to 10 mph. Chance of rain near 100 percent.

Tuesday: Occasional showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 65 to 84. East winds up to 15 mph. Chance of rain near 100 percent.

Tuesday Night: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

South Big Island

Rest Of Tonight: Breezy. Cloudy with occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 75 near the shore to around 55 near 5000 feet. Northeast winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 90 percent.

Tuesday: Cloudy and breezy. Numerous showers and slight chance of thunderstorms in the morning, then scattered showers in the afternoon. Highs around 84 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Tuesday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 74 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Puna

Rest Of Tonight: Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 65 to 72 near the shore to 57 to 63 at 4000 feet. Southeast winds up to 10 mph. Chance of rain near 100 percent.

Tuesday: Occasional showers and slight chance of thunderstorms in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 78 to 84 near the shore to around 66 at 4000 feet. East winds up to 10 mph. Chance of rain near 100 percent.

Tuesday Night: Occasional showers. Lows 63 to 70 near the shore to 53 to 59 at 4000 feet. Northeast winds around 10 mph. Chance of rain near 100 percent.

Waikoloa

Rest Of Tonight: Cloudy with occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 76 near the shore to around 57 above 4000 feet. Light winds. Chance of rain 80 percent.

Tuesday: Partly sunny with scattered showers. Highs 84 to 89 near the shore to 66 to 71 above 4000 feet. Northeast winds up to 10 mph shifting to the north in the afternoon. Chance of rain 50 percent.

Tuesday Night: Partly cloudy with isolated showers. Lows around 74 near the shore to 51 to 56 above 4000 feet. Northeast winds up to 15 mph shifting to the east after midnight. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A surface trough and plume of tropical moisture will maintain the potential for locally heavy rain and a few thunderstorms over Maui and the Big Island through this evening and transition westward across Oahu and Kauai tomorrow. A cold front will approach the islands and progress part-way through the state on Wednesday into Thursday morning, then stall and dissipate as a new high builds to its north. This will bring a period of wet trades and breezy to locally windy conditions to the islands later this week into the weekend.

Discussion

The main forecast concern in the short-term is the ongoing threat of heavy rain and flash flooding, particularly for windward Big Island and Maui through tonight and then for Oahu and Kauai tomorrow as this surface trough moves across the island chain. Radar and satellite imagery show deep convection and heavy rain occurring along a surface trough's north-to-south oriented axis as it moves across the Big Island and into eastern Maui this afternoon with thunderstorms occurring mainly over windward slopes of the Big Island. Rainfall rates of 4+ inches/hour have been estimated by dual pol radar and rain gages across south and east portions of the Big Island from late this morning through the afternoon, likely leading to flash flooding for those areas and a Flash Flood Warning is currently in effect.
CIMSS MIMIC precipitable water imagery continues to show a broad area of 2+ inches of precipitable water around this trough axis that will continue to move on up through the island chain tomorrow. With the support of an upper level trough setting up over the state and increased atmospheric instability, the threat of heavy rainfall and localized flooding will continue through tomorrow, with a westward shift in areas of concern as the surface trough progresses. A Flood Watch remains in effect for Maui and the Big Island through tomorrow afternoon. Oahu and Kauai may see a brief period of heavy rain tomorrow before the trough dissipates, but confidence is not quite high enough to expand the Flood Watch to these islands. Otherwise, moderate to locally breezy trades are expected through this evening, then trades will weaken tomorrow with the approach of a cold front from the northwest.
Model guidance is coming into slightly better agreement on the progression of the next cold front that will approach the state from the northwest midweek. Both the ECMWF and the GFS have this front move down to somewhere near Maui County or the Big Island Wednesday evening into Thursday morning. Showers are expected along and ahead of this front, especially due to the lingering tropical moisture associated with the surface trough that will be sliding off to the west and dissipating at that time. The surface high pushing in behind the front will lead to a resurgence in the trades, with breezy to locally windy conditions developing by late Wednesday and holding into the weekend. Moisture caught up in these trades will bring periods of showers to mainly windward and mauka areas.
Models begin to diverge more significantly this weekend heading into early next week. For now, have kept a wet breezy to strong trade wind pattern through the end of the forecast period.

Aviation

Moderate to locally breezy east southeast winds are expected to weaken tonight. A surface trough near Maui County will stall near Kauai and Oahu Tuesday. Clouds and heavy showers associated with this feature have moved onto windward and southeast Big Island today. AIRMET Sierra for IFR conditions is posted for windward Big Island, and for tempo mountain obscuration over Maui. Expect reduced visibility and lower ceilings around the eastern half of the state tonight.
Clouds and showers will spread to Maui County before sunset, and then Oahu and Kauai early Tuesday. AIRMET Sierra (for mountain obscurations at a minimum) is likely follow the general westward progression of the trough. Isolated thunderstorms will be possible across the eastern half of the state through Tuesday. Turbulence and icing should only be significant in or around the heaviest showers or thunderstorms, and should not be enough coverage to warrant an AIRMET or SIGMET.

Marine

A weak surface trough passing over the Hawaiian Islands will keep the pressure gradient over the eastern half of the state tight enough to maintain small craft advisories for waters surrounding the Big Island, Maui, and Molokai through tomorrow morning. Locally heavy showers and isolated thunderstorms associated with this feature will persist through tomorrow afternoon and possibly beyond.
A weak front will move into the northwest coastal waters Tuesday night then stall over the central portion of the state on Wednesday bringing more wet and windy weather. The pressure gradient behind the front should be strong enough to support fresh trade winds into the coming week.
A series of gale force lows progressing across the north pacific will send multiple northwest and north swells towards the Hawaiian Islands. The current medium-period, moderate size northwest (330 degree) has already begun to subside. The High Surf Advisory for north and west facing shores has been canceled. The next northwest swell will fill in on Thursday, be of relatively short-period, and peak below High Surf Advisory heights. A longer period northwest swell is expected Friday and Saturday, and could reach advisory levels. A yet even larger swell is possible Sunday and Monday.
Short-period easterly waves will increase during the second half of the week in response to the strengthening trade wind flow.

HFO Watches/Warnings/Advisories

Flood Watch through Tuesday afternoon for Maui Windward West, Maui Leeward West, Haleakala Summit, Kona, Kohala, Big Island Interior, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
Small Craft Advisory until 6 AM HST Tuesday for Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov