Hilo

Today: Cloudy. Widespread showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs around 78 near the shore to 63 to 68 at 4000 feet. West winds up to 15 mph shifting to the east in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy with showers. Lows around 65 near the shore to around 51 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 90 percent.

Monday: Cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to 63 to 68 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny with isolated showers and thunderstorms in the morning, then mostly cloudy with scattered showers and isolated thunderstorms in the afternoon. Highs 78 to 83 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening. Lows 65 to 70 near the shore to around 52 near 5000 feet. Light winds. Chance of rain 40 percent.

Monday: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 78 to 83 near the shore to around 69 near 5000 feet. Light winds becoming west up to 10 mph in the afternoon. Chance of rain 50 percent.

Waimea

Today: Breezy. Mostly cloudy with scattered showers and isolated thunderstorms. Highs 62 to 78. East winds up to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 64 near the shore to 50 to 58 near 3000 feet. East winds up to 25 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 78 near the shore to 69 to 76 near 3000 feet. East winds up to 25 mph increasing to 15 to 25 mph in the afternoon. Chance of rain 70 percent.

Kohala

Today: Breezy. Mostly cloudy with scattered showers and isolated thunderstorms. Highs 62 to 78. East winds up to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 64 near the shore to 50 to 58 near 3000 feet. East winds up to 25 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 78 near the shore to 69 to 76 near 3000 feet. East winds up to 25 mph increasing to 15 to 25 mph in the afternoon. Chance of rain 70 percent.

South Big Island

Today: Windy. Mostly sunny with isolated showers and thunderstorms in the morning, then cloudy with scattered showers and isolated thunderstorms in the afternoon. Highs around 81 near the shore to around 70 near 5000 feet. East winds 10 to 30 mph decreasing to up to 30 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows around 67 near the shore to around 51 near 5000 feet. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 81 near the shore to around 70 near 5000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Puna

Today: Cloudy. Widespread showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs around 78 near the shore to 63 to 68 at 4000 feet. West winds up to 15 mph shifting to the east in the afternoon. Chance of rain 90 percent.

Tonight: Cloudy with showers. Lows around 65 near the shore to around 51 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 90 percent.

Monday: Cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to 63 to 68 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny with isolated showers and thunderstorms in the morning, then partly sunny with scattered showers and isolated thunderstorms in the afternoon. Highs around 80 near the shore to 64 to 71 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon. Gusts up to 40 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to 47 to 55 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Monday: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 80 near the shore to 64 to 71 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon. Gusts up to 40 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

An upper low over the state will maintain an unstable and moist airmass which will generate showers and isolated thunderstorms, with locally heavy rainfall, into this evening. Drier and more stable conditions will filter across the state to begin the work week, with trade winds focusing showers mainly across windward areas into next weekend.

Discussion

Current radar shows showers across the islands again this morning, with the largest concentration of showers focused along windward areas as locally breezy trade winds continue. Radar estimates suggest locally enhanced rainfall rates remaining embedded within some of the showers this morning. Lightning data shows a few strikes in the vicinity of the Big Island, over 200 miles north to northeast of Hilo, in an area of enhanced instability (Showalter Index (SW) around -2c). A few isolated strikes were also noted over interior Oahu earlier this morning.
Today through tonight…High pressure centered well northeast of the state will maintain moderate to locally breezy trades through tonight. An upper low centered across the state this morning, will slowly move eastward and become centered across the Big Island tonight through early Monday, while an upper ridge builds in across the western end of the state. This pattern will maintain deep layered moisture (PWs greater than 1.50″) and modest instability (SW around 0 to -1c) across the state this morning. This unstable airmass will then shift eastward and become mainly concentrated across the eastern end of the state this evening into early Monday. Corresponding thunderstorm probabilities show the best chance for isolated storms, remains around the Big Island along with windward zones and surrounding waters into this afternoon. Otherwise, drier and more stable conditions will begin to push in across the western end of the state later this afternoon. Overall, will maintain the current forecast trends, with showers and isolated thunderstorms lingering across a majority of the islands this morning/afternoon. Have also introduced a diminishing trend in the precipitation pattern this afternoon/evening across the western islands, to reflect drier and more stable conditions expanding into the region.
Monday and Tuesday…the transition toward stable and dry conditions will continue, as the upper low weakens and exits eastward of the state. High pressure drifting well north of the region will further reinforce the trade wind weather pattern across the islands to begin the work week. Current data solutions suggest enough moisture lingering around the islands (modeled PW values 1.25 to 1.35″, moisture depths 9k-13k ft) to maintain increased areal coverage of showers across windward locations into early Tuesday. Showers will remain focused across mainly windward areas. However the airmass will quickly stabilize through the beginning of the week, which will greatly reduce the threat of locally heavy rainfall.
Wednesday into next weekend…the airmass continues to become more dry and more stable through the period, with forecast PW values falling to under 1.00″ while modeled moisture depths fall to around 8k ft or less. This pattern will greatly reduce the intensity and areal coverage of showers across the islands. Lingering trade wind flow will maintain showers to mainly favored windward locations, with the most persistent shower coverage at night through early morning.

Aviation

Breezy easterly trade winds will prevail through the 24-hr forecast period, with clouds and showers favoring windward areas. Showery conditions will continue through the morning hours today, with some becoming heavy and spilling into leeward areas due to plenty of moisture and an upper trough in the area. The added instability associated with the upper trough will also support a few thunderstorms today. A return of drier air and more stable trade wind conditions is expected tonight into Monday.
AIRMET Sierra for tempo mountain obscuration for most windward areas will persist through the morning hours.
AIRMET Tango for moderate low-level turbulence will continue over and downwind of island mountains.

Marine

A strong high pressure system north of the Hawaii region will continue to drift eastward producing fresh to locally strong trade winds over the coastal waters through the week. An upper level low over the eastern islands will continue to slowly drift eastward today. This low will enhance shower activity mainly over southern and eastern waters today before drifting away from the region on Monday. A Small Craft Advisory (SCA) was cancelled for most leeward waters and all waters around Kauai this morning. The SCA remains in effect for most waters around Maui and Hawaii Counties due to strong winds. Weather conditions will become more stable today, although isolated thunderstorms may linger into the evening hours.
A medium period north-northwest swell (340-350 degrees) will decline today lowering surf heights along north and west facing shores. On Monday, the next long period northwest swell (310-320 degrees) will slowly fill in, and peak on Tuesday and Wednesday. On Thursday, two overlapping swells will build into the region. A new long period northwest (320-330 degree) swell will arrive by Thursday morning, while a trailing medium period north (350-360 degree) swell fills in by Thursday night. These two swells may boost surf heights to near advisory levels for exposed north and west facing shores on Thursday and Friday. Surf along east facing shores will remain choppy and small through the week as a belt of fresh to strong easterly trades continues to blow across the region. Surf along south facing shores will also remain on the small side.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Oahu Windward Waters, Kaiwi Channel, 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