Hilo

Today: Showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 74. Light and variable wind. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 61. Light and variable wind. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Monday: Scattered showers. Partly sunny, with a high near 77. Calm wind becoming east 5 to 7 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a high near 77. Light and variable wind. Chance of precipitation is 60%. New rainfall amounts between a half and three quarters of an inch possible.

Tonight: Showers likely and possibly a thunderstorm before 8pm, then isolated showers and thunderstorms after 8pm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 59. Calm wind. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Monday: Scattered showers. Partly sunny, with a high near 79. Calm wind becoming west northwest around 5 mph. Chance of precipitation is 40%. New precipitation amounts between a quarter and half of an inch possible.

Waimea

Today: Showers and possibly a thunderstorm before noon, then scattered showers and thunderstorms after noon. Some of the storms could produce heavy rainfall. High near 71. North northeast wind around 5 mph becoming calm in the afternoon. Chance of precipitation is 80%. New rainfall amounts between 1 and 2 inches possible.

Tonight: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 50. Calm wind. Chance of precipitation is 50%. New rainfall amounts between three quarters and one inch possible.

Monday: Showers likely. Mostly cloudy, with a high near 74. Light and variable wind. Chance of precipitation is 70%. New precipitation amounts between three quarters and one inch possible.

Kohala

Today: Showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 67. West southwest wind around 5 mph becoming calm in the afternoon. Chance of precipitation is 90%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 43. Light and variable wind. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Monday: Scattered showers. Partly sunny, with a high near 70. Light and variable wind. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Showers likely and possibly a thunderstorm before noon, then scattered showers and thunderstorms after noon. Some of the storms could produce heavy rainfall. Partly sunny, with a high near 79. Breezy, with an east wind 11 to 16 mph, with gusts as high as 21 mph. Chance of precipitation is 60%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 69. East wind 10 to 14 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Monday: Scattered showers. Mostly sunny, with a high near 79. East wind 9 to 13 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Puna

Today: Showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 74. Calm wind becoming south 5 to 7 mph in the afternoon. Chance of precipitation is 100%. New rainfall amounts between three quarters and one inch possible.

Tonight: Showers likely and possibly a thunderstorm. Some of the storms could produce heavy rainfall. Mostly cloudy, with a low around 59. South southwest wind 3 to 7 mph. Chance of precipitation is 70%. New rainfall amounts between three quarters and one inch possible.

Monday: Scattered showers. Partly sunny, with a high near 76. Calm wind becoming southeast 5 to 7 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Waikoloa

Today: Showers likely and possibly a thunderstorm before noon, then scattered showers and thunderstorms after noon. Some of the storms could produce heavy rainfall. Partly sunny, with a high near 76. Light and variable wind becoming north northwest 5 to 8 mph. Chance of precipitation is 60%. New rainfall amounts between a half and three quarters of an inch possible.

Tonight: Scattered showers and thunderstorms before 8pm. Some of the storms could produce heavy rainfall. Mostly clear, with a low around 59. Light and variable wind. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Monday: Scattered showers. Partly sunny, with a high near 80. Calm wind becoming west northwest 5 to 7 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Detailed Forecast

Synopsis

A low pressure system northeast of the islands and a surface trough over the eastern islands will keep wet weather and isolated thunderstorms in the forecast today. Heavy rains from developing showers and saturated ground conditions will keep an elevated flood threat through the afternoon hours. Expect a gradual drying trend from Monday onward. Moderate to breezy trade winds will blow through Niihau and Kauai today with decreasing trade winds over Oahu. Lighter winds are expected for the eastern islands with decreasing wind speed trends through Monday as a surface trough drifts westward across the island chain. Trade winds will slowly strengthen from Tuesday through Friday becoming breezy by the end of the week.

Discussion

An unstable pattern continues over the Hawaiian Islands today as a low pressure system northeast of Oahu and a surface trough over the eastern islands keeps showers and thunderstorms in the short range forecast. The Flash Flood Watch was extended statewide through the afternoon due to the lingering instability, saturated ground, and heavy shower potential. A strong 1040 MB high pressure system far northwest of the state is producing moderate to breezy trade winds today over Niihau and Kauai. A surface trough moving slowly westward from Maui to Kauai today will decrease wind speeds statewide through Monday. Lighter large scale winds will allow local scale land and sea breezes to develop today and tomorrow.
For the Big Island summits today, expect gusty winds along with a wintry mix as snow showers from the upper level low are forecast over the highest slopes of Mauna Kea and Mauna Loa above 11,000 feet elevation. Strong winds with gusts up to 65 MPH will produce blowing and drifting snow on area roadways with reduced visibility.
The low pressure system northeast of the islands and a surface trough over the eastern islands will weaken over the next 24 hours, with increasing stability aloft and a gradual statewide drying trend from Monday onward.. The surface trough near Maui will drift westward into Oahu by tonight, decreasing winds statewide through Monday. High pressure building in from the north will increase stability and trade winds from Tuesday through Friday. Strengthening trade winds will support brief passing showers through the week favoring windward and mountain areas. These showers will not be nearly as unstable or heavy as we saw this past week. One wrinkle in this forecast shows up by Tuesday night as a remnant cloud band from an old cold front drifts into the state from the north, enhancing shower activity a bit through Wednesday. Unstable portions of this cloud band may linger over Hawaii County a bit longer, enhancing showers along the windward slopes of the Big Island into Friday.
A high pressure system passing far north of the state this weekend will keep breezy winds and periods of showers in the forecast.

Aviation

Unsettled weather will continue across the islands today as a low pressure system, surface and aloft, remains in the island vicinity. Periods of MVFR cigs/vsbys can be expected and isolated IFR conditions will be possible in showers. The most likely areas to see cig/vsby reductions will be in windward areas, but will also affect leeward areas at times. Conditions should begin to improve tonight as the airmass begins to stabilize.
AIRMET Sierra remains in effect for mountain obscuration across Maui County, and windward sections of Oahu and Kauai. Conditions should improve across Maui County and Oahu later this morning, but will likely continue for much of the day across Kauai. AIRMET Tango remains in effect for low level turbulence over and downwind of Kauai. This AIRMET will likely remain in place today.

Marine

A dissipating front has stalled near the Big Island this morning. This boundary will become an east-to-west moving surface trough that will weaken winds across most of the coastal waters east of the trough through Monday morning. Fresh trades will blow west of the trough across the far northwestern waters with light to gentle easterlies east of the trough into Tuesday. High pressure will build north of the islands through mid to late week and tighten the pressure gradient enough to re-establish areawide moderate to locally strong trades Thursday through next weekend. Due to elevated seas from this weekend’s larger north swells and a lingering east wind wave swell, a Small Craft Advisory (SCA) remains in effect for all waters except Maalaea Bay and the Big Island’s leeward waters through Monday. SCA conditions may hold through much of next week to account for the combination of both strengthened trades and high seas.
Dominant north-northeast swells will build and maintain surf at or above advisory levels across Niihau, Kauai, Oahu, Molokai, Maui and the Big Island’s northern and eastern exposures, including Maui’s west-facing coastline due to northerly wrap, the next couple of days. These swells will hold through the day and will slowly diminish through Tuesday. This moderate north swell, along with a lingering easterly wind swell, has extended the High Surf Advisory (HSA) for these coastlines through Monday night. Surf should fall below advisory thresholds along north and east-facing shorelines and west-facing Maui shores Tuesday morning. Additionally, due to the more due north swell direction, a Marine Weather Statement has been issued for surges that may occur at north-facing harbor entrances through the day, particularly Kahului and Hilo Harbors.
Recent east swells will gradually lower through Monday as trades weaken just upstream of the chain. The next low, moderate period northwest swells are scheduled to pass around the islands during mid to late week. A more typical short period trade wind swell will return during the latter part of the week in response to restrengthening trades over and upstream of the islands. Surf along south-facing shores will remain at more seasonable levels the next few days as low Southern Hemispheric moderate period swells reach the state.

HFO Watches/Warnings/Advisories

Flash Flood Watch through this afternoon for all Hawaii islands.
High Surf Advisory until 6 PM HST Monday for Niihau, Kauai Windward, Kauai Leeward, Oahu North Shore, Oahu Koolau, Olomana, Molokai, Maui Windward West, Maui Leeward West, Maui Central Valley, Windward Haleakala, Big Island North and East.
Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 PM HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov