Hilo

Today: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 77. Calm wind becoming east northeast 5 to 7 mph. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers and thunderstorms, then showers likely and possibly a thunderstorm after midnight. Mostly cloudy, with a low around 59. Calm wind becoming west around 5 mph after midnight. Chance of precipitation is 70%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Monday: Showers likely and possibly a thunderstorm before noon, then scattered showers and thunderstorms after noon. Partly sunny, with a high near 76. Calm wind becoming north northeast 5 to 7 mph in the afternoon. Chance of precipitation is 70%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Kona

Today: Isolated showers and thunderstorms after noon. Some of the storms could produce heavy rainfall. Mostly sunny, with a high near 79. Calm wind becoming west southwest 5 to 7 mph. Chance of precipitation is 20%.

Tonight: Scattered showers and thunderstorms before midnight, then isolated showers. Mostly cloudy, with a low around 59. Light and variable wind. Chance of precipitation is 30%.

Monday: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 78. Calm wind becoming west southwest around 6 mph. Chance of precipitation is 40%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Waimea

Today: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 74. Calm wind becoming west around 6 mph. Chance of precipitation is 40%. New rainfall amounts between a half and three quarters of an inch possible.

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 50. Calm wind becoming east northeast 5 to 7 mph after midnight. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Monday: Scattered showers and thunderstorms, then showers likely and possibly a thunderstorm after noon. Partly sunny, with a high near 73. North northeast wind 6 to 13 mph. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Kohala

Today: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 70. West wind 5 to 9 mph becoming calm in the afternoon. Chance of precipitation is 40%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers and thunderstorms, then showers likely and possibly a thunderstorm after midnight. Mostly cloudy, with a low around 43. Calm wind becoming northeast 5 to 8 mph after midnight. Chance of precipitation is 70%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Monday: Showers likely and possibly a thunderstorm. Partly sunny, with a high near 69. Northeast wind 5 to 9 mph. Chance of precipitation is 70%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

South Big Island

Today: Isolated showers and thunderstorms after noon. Some of the storms could produce heavy rainfall. Sunny, with a high near 79. East southeast wind 5 to 8 mph becoming calm in the afternoon. Chance of precipitation is 20%.

Tonight: Isolated showers and thunderstorms. Some of the storms could produce heavy rainfall. Partly cloudy, with a low around 67. Light and variable wind becoming northeast 5 to 10 mph in the evening. Chance of precipitation is 20%.

Monday: Scattered showers, mainly after noon. Mostly sunny, with a high near 78. Northeast wind 6 to 11 mph. Chance of precipitation is 30%.

Puna

Today: Scattered showers, with thunderstorms also possible after noon. Mostly cloudy, with a high near 76. Calm wind becoming north northwest 5 to 7 mph in the afternoon. Chance of precipitation is 50%. New rainfall amounts between a half and three quarters of an inch possible.

Tonight: Scattered showers and thunderstorms, then showers likely and possibly a thunderstorm after midnight. Mostly cloudy, with a low around 59. North northwest wind 5 to 7 mph becoming light and variable. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.

Monday: Showers likely and possibly a thunderstorm. Partly sunny, with a high near 75. West wind 5 to 8 mph becoming north northeast in the morning. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Waikoloa

Today: Isolated showers, then scattered showers and thunderstorms after noon. Partly sunny, with a high near 80. Light and variable wind becoming west northwest 6 to 11 mph in the afternoon. Chance of precipitation is 40%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers and thunderstorms, mainly before midnight. Mostly clear, with a low around 59. Light and variable wind becoming east southeast 5 to 8 mph after midnight. Chance of precipitation is 30%.

Monday: Scattered showers and thunderstorms, mainly after noon. Mostly sunny, with a high near 79. East northeast wind 5 to 9 mph becoming calm in the afternoon. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Detailed Forecast

Synopsis

Unsettled weather is possible through Monday as a trough aloft passes over the area, bringing the potential for thunderstorms and a few locally heavy downpours. Trades will redevelop over Kauai and Oahu on today, then gradually strengthening statewide early next week.

Discussion

An upper level trough will move southeast across the state today. A surface low and trough located northeast of the state has cut off the trade wind flow over much of the state. Infrared satellite shows some midlevel clouds passing over Maui County, while scattered low clouds and showers are spread out across the state.
The upper trough axis will move across Oahu this morning, Maui midday, Big Island tonight, and then linger across the eastern end of the state through Monday. 500 mb temperatures along the trough axis will be -16 C and 700 mb temperature around 1 C. Precipitable water (PW) values will remain around normal for this time of year, 1.2 inches. Given the dynamic forcing and instability produced by the upper trough, thunderstorms will be possible for most of the state today, then across Maui County and the Big Island Monday.
The greatest threat for thunderstorms over the islands will be during peak heating today where the strong upward forcing will get a nice boost from surface heating. As it stands the most favorable superposition of both looks to be Molokai through Big Island in the Noon-6pm HST time period. Oahu resides on the fringe of the best potential given that the best forcing will swing through slightly earlier in the day, but conditions will still be favorable enough to retain mention of thunderstorms. Small hail is also in play within any stronger updrafts. However, the progressive nature of the event coupled with relatively low PW values around 1.1 to 1.2 inches will likely preclude the threat of widespread heavy rainfall that would lead to significant flooding. Finally, cold mid-level temperatures will support episodic snow showers for the Big Island summits and Haleakala, down to around 10000 ft, whenever deep convection moves over those areas.
The upper trough will slide east of the area on Tuesday. Trades will continue to build in west to east as the surface lows move away from the area. Mostly dry and stable trade winds weather in place Wednesday and Thursday. A weak backdoor cold front may move into the area from the north around Friday.

Aviation

A mainly light background north to northeast low level wind flow will prevail through today. The flow will be light enough for a daytime sea breeze to develop this morning over the interior and lee areas of the smaller islands. There is also an upper level trough with cold temperatures at the mid level dropping down on the islands today. The light winds, upper level disturbance, along with daytime heating, will lead to an active afternoon of scattered showers and the chance of thunderstorms for Maui and the Big Island. AIRMET Sierra for mountain obscuration is possible across the windward and mountain sections of all islands, and the Kona slopes of the Big island. Some of these showers and storms may linger through the early evening hours, but most will be done by midnight. Firmer moderate northeast trades will follow in through the rest of tonight.
Light rime icing was reported by a couple of aircraft between 14k and 17k feet from a large patch of layered mid and high clouds that formed quickly between 08z and 10z over the central islands. The base of this deck is around 10k feet, and will be passing through most of the Big Island in the coming hours. We anticipate these clouds to thin out by 20z. AIRMET Zulu is covering for this icing.

Marine

Light to moderate north-northeast winds (stronger Kauai and Oahu waters) will continue into tonight due to a persistent trough/low lurking northeast of the state. Winds should remain light enough for the land and sea breeze regime to continue for most sheltered coastal areas today. In addition to light winds, a few heavy showers and thunderstorms will become a possibility today as an upper disturbance drops south into the area – best chance windward waters and eastern half of the state. Northeast trade winds will return through the first half of the week, potentially reaching the fresh to locally strong category by midweek.
Surf along south facing shores will gradually rise tonight into Monday as a long-period, south-southwest swell arrives. This source will peak below the advisory level Monday through Tuesday, then slowly lower through midweek.
Surf along north and west facing shores will trend up tonight through the first half of the week as a small, west-northwest swell arrives from a gale that developed near the Kurils a few days ago. Although confidence remains low, a moderate, short- period north-northeast swell is depicted later in the week due a strong gradient setting up once again to the north between strong high pressure near the Date Line and low pressure to its east.
Surf along east facing shores will remain small through the first half of the week, then trend up by the second half along exposed coasts as the previously discussed north-northeast swell arrives.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov