Hilo

Tonight: Mostly cloudy with scattered showers. Lows 64 to 71 near the shore to 54 to 61 at 4000 feet. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 79 to 84 near the shore to 64 to 69 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 52 to 58 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with isolated showers. Haze. Lows around 74 near the shore to around 54 near 5000 feet. Light winds. Chance of rain 20 percent.

Tuesday: Partly sunny. Haze through the day. Scattered showers in the afternoon. Highs 84 to 89 near the shore to around 69 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy. Scattered showers in the evening. Haze through the night. Lows around 73 near the shore to around 53 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Mostly cloudy with scattered showers. Haze through the night. Lows 64 to 73 near the shore to 58 to 65 near 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Tuesday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Haze through the day. Highs 64 to 85. East winds 10 to 20 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy with isolated showers. Haze through the night. Lows 63 to 72 near the shore to 55 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Kohala

Tonight: Mostly cloudy with scattered showers. Haze through the night. Lows 64 to 73 near the shore to 58 to 65 near 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Tuesday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Haze through the day. Highs 64 to 85. East winds 10 to 20 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy with isolated showers. Haze through the night. Lows 63 to 72 near the shore to 55 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Big Island

Tonight: Mostly cloudy. Breezy and haze. Lows around 75 near the shore to around 57 near 5000 feet. Northeast winds up to 20 mph.

Tuesday: Partly sunny. Breezy. Haze through the day. Isolated showers in the afternoon. Highs around 86 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tuesday Night: Mostly cloudy. Breezy. Isolated showers in the evening. Haze through the night. Lows around 74 near the shore to around 56 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy with scattered showers. Lows 64 to 71 near the shore to 54 to 61 at 4000 feet. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 79 to 84 near the shore to 64 to 69 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 52 to 58 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly cloudy. Isolated showers in the evening. Haze through the night. Lows around 76 near the shore to 53 to 58 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Breezy. Haze through the day. Isolated showers in the afternoon. Highs 84 to 89 near the shore to 67 to 73 above 4000 feet. North winds up to 20 mph. Chance of rain 20 percent.

Tuesday Night: Partly cloudy in the evening then becoming mostly cloudy. Haze. Lows around 74 near the shore to 52 to 57 above 4000 feet. Northeast winds up to 10 mph.

Detailed Forecast

Synopsis

A moderate easterly trade wind flow will gradually become more stable tonight and Tuesday, as an area of low pressure west of Kauai moves away from the area. Showers will favor windward slopes, and while most leeward areas will be rather dry, spotty afternoon showers will develop along the Kona slopes of the Big Island. Trade winds will start to weaken on Thursday and will likely be disrupted on Friday, when a passing upper level disturbance is expected to produce isolated interior showers during the afternoon. A weakening front may move down portions of the island chain this weekend.

Discussion

The trade wind flow is slowly stabilizing as an upper-level low west of Kauai drifts away from the region. This feature triggered some impressive showers on Kauai early Sunday, but a ridge aloft building in from the east is producing increasingly stable conditions this afternoon. Scant shower activity has been observed over windward areas from Kauai to Molokai today, but a small pocket of moisture dropped less than a quarter of an inch of rainfall on windward Big Island and Maui and fueled a few showers over interior sections of the Big Island. Expect this shower activity to diminish overnight, with light rainfall accumulations over windward slopes.
A moderate and rather stable trade wind flow will prevail by Tuesday. High pressure at 500 mb centered overhead will lead to a strengthening inversion that will produce stability, but the departing upper low will send a shield of high clouds over the island chain. The surface ridge north of the state will remain essentially unchanged and generate moderate trade winds. Guidance shows little organized moisture in the trade flow, which points toward modest windward rainfall along with a few afternoon showers across the leeward slopes of the Big Island. Drier and increasingly stable conditions favor a decrease in showers on Wednesday.
Trade winds will start to decline on Thursday, as an approaching North Pacific front weakens the surface ridge north of Hawaii. The ridge aloft over the islands will hang on through the day, suggesting continued stable conditions and limited rainfall.
Trade winds will likely become disrupted Thursday night and Friday as the front advances. A fast-moving upper-level trough passing over the island chain will lead to some instability, but moisture may be lacking. As a result, day time sea breezes will likely lead to spotty interior showers Friday afternoon.
The shallow and weakening front may reach Kauai sometime Saturday and drift over other portions of the island chain Sunday. Timing with this feature remains highly uncertain, and the GFS and ECMWF show the above mentioned upper-level trough lifting to the northeast with ridging aloft build over the islands during this time. Since the frontal band will be very weak with no upper support, rainfall will likely be confined to windward and north slopes with little threat for flooding.

Aviation

Moderate trades will continue for the next couple of days as ridge builds north of the state. High clouds will stream in from the southwest tonight. Low clouds and showers will remain over windward and southeast Big Island this evening bringing brief mountain obscurations along these slopes. No AIRMETs expected tonight, but will monitor for lower ceilings, visibilties and extensive mountain obscuration on the Big Island.

Marine

A surface ridge of high pressure far north of the state will maintain moderate to fresh trade winds through tonight. A trough and upper level disturbance west of the offshore waters will continue to produce isolated thunderstorms across the south and west offshore waters for a few more days. Moderate to fresh trade winds will strengthen slightly into the fresh to locally strong range from Tuesday through Thursday then steadily decline Thursday night as the ridge shifts southeastward towards the state in advance of an approaching cold front.
A large reinforcing short to medium period north swell that quickly filled in last night peaked this morning and will continue to decline through Tuesday. With the large north swell declining this afternoon, surf heights have dropped below High Surf Advisory thresholds for select north and east facing shores and seas have also dropped below Small Craft Advisory thresholds.
A gale low currently passing far north of the state will send the next large medium period north-northwest swell. This swell should arrive Tuesday night into Wednesday and peak late Wednesday. Surf heights should reach advisory thresholds along north and west facing shores by Wednesday afternoon. Advisory level surf could hold into parts of the day Thursday, but the swell should be on a steady decline. A reinforcing north-northwest swell is possible on Friday, which should help maintain moderate surf on Friday.
In the long range, a deep low pressure system is expected to develop to our north and northeast Friday into Saturday. This low will likely send a large north-northeast (020-030 degree) swell late this weekend. Due to the swell angle, heavy surges will be possible along north facing harbors such as Kahului and Hilo on Sunday.
Surf along select east facing shores will remain elevated due to the declining north swell through tonight. A large north-northeast swell on Sunday could bring advisory level surf along east facing shores on Sunday. South facing shores will remain small throughout this week. A small long- period south- southwest swell is possible Friday into the weekend with a larger out of season south swell possible early next week.

Fire weather

Relative humidity values and winds will be below critical fire weather conditions into the weekend. A weak inversion near the Big Island and Maui will strengthen and become better defined near 7,000 feet Tuesday then build down to around 5,000 feet Wednesday.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov