Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers and thunderstorms in the morning, then partly sunny with scattered showers and isolated thunderstorms in the afternoon. Highs around 79 near the shore to around 67 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows around 68 near the shore to around 57 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs around 80 near the shore to around 68 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs around 78. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 69. Northeast winds around 15 mph. Chance of rain 30 percent.

Monday: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 79. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Cloudy and breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Cloudy with scattered showers. Lows 57 to 62 in the valleys to around 51 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Monday: Breezy. Cloudy with scattered showers. Highs 67 to 75 in the valleys to around 62 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 71 to 78. East winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 69. East winds up to 15 mph. Chance of rain 30 percent.

Monday: Partly sunny with scattered showers. Highs 72 to 79. East winds up to 15 mph. Chance of rain 40 percent.

East Kaua’i

Today: Cloudy with numerous showers and isolated thunderstorms. Highs 71 to 78. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 58 to 70. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Monday: Mostly cloudy with scattered showers. Highs 72 to 79. Northeast winds 10 to 15 mph. Chance of rain 50 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.

Data Courtesy of NOAA.gov