Hilo

Today: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 74. West wind 5 to 9 mph becoming east northeast in the afternoon. Chance of precipitation is 100%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Occasional showers and possibly a thunderstorm. Low around 62. North northeast wind 6 to 9 mph becoming west after midnight. Chance of precipitation is 100%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Monday: Occasional showers. High near 74. West wind 5 to 9 mph becoming northeast in the afternoon. Chance of precipitation is 100%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Isolated showers, then scattered showers and thunderstorms after noon. Partly sunny, with a high near 78. Calm wind becoming west southwest 5 to 9 mph in the afternoon. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms before midnight, then isolated showers. Mostly cloudy, with a low around 60. Southwest wind 5 to 7 mph becoming light and variable. Chance of precipitation is 40%. New precipitation amounts between a quarter and half of an inch possible.

Monday: Scattered showers after noon. Partly sunny, with a high near 78. West southwest wind 5 to 10 mph becoming light and variable in the afternoon. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Waimea

Today: Showers likely, with thunderstorms also possible after noon. Some of the storms could produce heavy rainfall. Partly sunny, with a high near 73. Windy, with a northeast wind 17 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 70%. New rainfall amounts between three quarters and one inch possible.

Tonight: Showers likely and possibly a thunderstorm. Mostly cloudy, with a low around 51. Windy, with an east northeast wind 22 to 24 mph, with gusts as high as 36 mph. Chance of precipitation is 60%. New precipitation amounts between three quarters and one inch possible.

Monday: Occasional showers. High near 73. Windy, with a northeast wind 21 to 25 mph, with gusts as high as 36 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.

Kohala

Today: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 69. Very windy, with an east wind around 31 mph, with gusts as high as 50 mph. Chance of precipitation is 80%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Occasional showers and possibly a thunderstorm. Low around 44. Very windy, with an east wind around 31 mph, with gusts as high as 50 mph. Chance of precipitation is 100%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Monday: Occasional showers. High near 69. Very windy, with an east wind 26 to 31 mph, with gusts as high as 50 mph. Chance of precipitation is 100%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 78. Windy, with an east northeast wind 24 to 29 mph, with gusts as high as 37 mph. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely and possibly a thunderstorm before midnight, then isolated showers. Mostly cloudy, with a low around 68. Very windy, with an east northeast wind 28 to 31 mph, with gusts as high as 40 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Monday: Scattered showers, mainly after noon. Partly sunny, with a high near 78. Very windy, with an east northeast wind 28 to 31 mph, with gusts as high as 40 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Puna

Today: Occasional showers and possibly a thunderstorm. Some of the storms could produce heavy rainfall. High near 73. Northwest wind 6 to 11 mph becoming east northeast in the afternoon. Chance of precipitation is 100%. New rainfall amounts between 1 and 2 inches possible.

Tonight: Occasional showers and possibly a thunderstorm. Low around 60. Northeast wind 10 to 13 mph. Chance of precipitation is 100%. New rainfall amounts between three quarters and one inch possible.

Monday: Occasional showers. High near 73. Breezy, with a northeast wind 11 to 15 mph, with gusts as high as 20 mph. Chance of precipitation is 100%. New precipitation amounts between a quarter and half of an inch possible.

Waikoloa

Today: Scattered showers and thunderstorms after noon. Mostly sunny, with a high near 79. Windy, with an east southeast wind 6 to 11 mph becoming east northeast 20 to 25 mph in the morning. Winds could gust as high as 50 mph. Chance of precipitation is 30%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms before midnight. Partly cloudy, with a low around 60. Very windy, with an east northeast wind 25 to 31 mph, with gusts as high as 50 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Monday: Isolated showers after noon. Mostly sunny, with a high near 79. Very windy, with an east northeast wind 21 to 31 mph decreasing to 11 to 21 mph in the afternoon. Winds could gust as high as 50 mph. Chance of precipitation is 20%.

Detailed Forecast

Synopsis

A trough aloft will keep the island atmosphere unstable through much of the week, keeping a wetter than normal trade wind pattern in place. Showers will favor windward and mauka areas with a few showers spreading leeward from time to time. Locally heavy rainfall and thunderstorms will be possible across portions of Maui and the Big Island today. In addition to the showery pattern, trade winds will strengthen today, with windy conditions expected to persist through Tuesday. The trades will then ease to moderate to locally breezy levels during the middle to latter part of the week.

Discussion

Currently at the surface, a 1035 mb high is centered around 1150 miles northeast of Honolulu, while another 1044 mb high is centered around 1300 miles north of Kauai. The resulting gradient is producing breezy trade winds across the island chain early this morning. Infrared satellite imagery shows mostly cloudy conditions in windward areas, with partly cloudy skies prevailing in leeward locales. Radar imagery shows scattered to numerous showers moving into windward and mauka areas, with a few showers making it into leeward sections of the smaller islands from time to time. Main short term concerns continue to revolve around the ongoing Flash Flood and Winter Weather headlines, as well as the potential need for Wind Advisories.
High pressure northeast of the state will become absorbed into a building surface high north of the state today. This new high will then settle slowly southward while weakening slightly Monday through Tuesday. A new strong surface high will build northwest of the state Wednesday through Friday, then shift eastward far to the north of the island chain next weekend. Overall, breezy to windy trades will continue through the first half of the week, with the trades peaking this afternoon through early Tuesday. The strengthening trade are expected to boost wind speeds to advisory levels across portions of Maui County this afternoon through at least Monday, so a Wind Advisory has been posted for these areas. As the trades peak on Monday, the Wind Advisory may need to be expanded to include much, if not all of the island chain. Additionally, the Wind Advisory may need to be extended in time through Tuesday for some of the typically windier areas of Maui County and the Big Island. The trades should ease a bit for the middle and latter part of week as the gradient relaxes, but will likely hold in the moderate to locally breezy range.
As for the remaining weather details, a trough aloft will keep a moist and unstable airmass over the state today and tonight. The deepest moisture and most unstable conditions will reside over the eastern islands of Maui and the Big Island however, where the threat for locally heavy rainfall and thunderstorms will continue, mainly over windward areas. The Flash Flood Watch remains in effect until 6 PM this evening, but this may eventually need to be extended through early Monday morning. Across the remainder of the state, a wet trade wind pattern is expected with showers favoring windward and mauka areas and a few showers spreading leeward from time to time.
Due to the moisture depth extending above the high elevation summits of Mauna Kea and Mauna Loa, a Winter Weather Advisory remains in effect for a wintry mix of freezing rain/drizzle and snow through 6 AM Monday.
The upper trough axis will shift south of the state on Monday, then linger just south of the islands through mid week. A series of shortwave troughs may then rotate through the region Thursday through next weekend. Overall, with troughing aloft more or less being maintained over the state through much of the week, we should see a wetter than normal trade wind pattern prevailing with showers favoring windward and mauka areas and a few showers reaching leeward communities from time to time.

Aviation

An east-west oriented upper trough remains over the island chain this morning. This is causing widespread MVFR ceilings and showers for eastern sections of the Big Island, where AIRMET Sierra remains in effect for tempo mountain obscuration from Upolu Point to Cape Kumukahi to South Cape. Early morning satellite and radar imagery also shows an increase in shower activity and clouds along east sections of the smaller islands, so AIRMET Sierra also accounts for tempo mountain obscuration in these areas as well. These conditions should begin improving later this morning by around 18z.
The wet pattern will continue throughout the day, especially for the Big Island. Daytime heating and the unstable air mass could result in a few thunderstorms on the leeward side of the Big Island this afternoon and early evening. Elsewhere, scattered showers will favor windward and mountain areas, causing tempo MVFR conditions at times.
Breezy to locally strong easterly trade winds will continue today as a strengthening surface high builds north of the state. AIRMET Tango remains in effect to account for low-level mechanical turbulence over and immediately south through west of the mountains for all islands. As the winds strengthen, it is possible that AIRMET Tango will also be needed for sustained surface winds of 30kts or greater by tonight, particularly for the Alenuihaha Channel and waters south of the Big Island.

Marine

Strong trade winds will continue into the middle of the week, resulting in a Small Craft Advisory (SCA), Gale Warning, and High Surf Advisory for east facing shores.
A high pressure system to the far northeast will be reinforced by a high pressure far to the north. The high to the north is expected to becoming the dominant of the two systems over the next 24 hours. The pressure gradient over the region will strengthen, resulting in an uptick in winds over the coastal waters. The typical windier areas have been placed under a Gale Warning starting at 6pm tonight as a result. A SCA is in effect for all waters today, and then will be in place for the remaining waters not under the Gale Warning starting tonight. Seas will also remain above the 10 ft SCA levels. Winds are forecast to start to back off some on Wednesday, so will likely see some changes to the Gale/SCA areas at that point.
The persistent trade wind pattern we have been experiencing over the last several days has already been generating advisory level surf along east facing shores. The current High Surf Advisory for east facing shores continues through Tuesday, although its possible that it may need to be extended.
A small to moderate northwest swell is expected to begin to decline today. The next northwest swell is expected to arrive Wednesday night and currently is expected to run higher than the current swell. This swell could raise surf to near advisory levels as it peaks Thursday. A small bump is likely along south facing shores Monday night into Wednesday, and again at the end of the week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Tuesday for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, South Big Island, Big Island North and East.
Flash Flood Watch through this afternoon for Maui Windward West, Windward Haleakala, Haleakala Summit, South Big Island, Big Island North and East, Big Island Interior.
Wind Advisory from noon today to 6 PM HST Monday for Molokai, Lanai, Kahoolawe, Maui Windward West, Maui Leeward West, Maui Central Valley, Windward Haleakala, Leeward Haleakala, South Big Island, Big Island North and East, Kohala.
Winter Weather Advisory until 6 AM HST Monday for Big Island Summits.
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Warning from 6 PM this evening to 6 PM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Tuesday 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, Big Island Windward Waters.

Data Courtesy of NOAA.gov