Hilo

Today: Isolated showers, then scattered showers and thunderstorms after noon. Some of the storms could produce heavy rain. Widespread haze. Mostly sunny, with a high near 77. West northwest wind 5 to 7 mph becoming light and variable in the afternoon. Chance of precipitation is 40%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers. Mostly cloudy, with a low around 62. Light and variable wind. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Scattered showers. Partly sunny, with a high near 77. North wind 3 to 8 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Isolated showers, then scattered showers and thunderstorms after noon. Some of the storms could produce heavy rain. Mostly sunny, with a high near 79. South southeast wind 9 to 14 mph becoming light and variable. Winds could gust as high as 20 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. The rain could be heavy at times. Widespread haze after midnight. Mostly cloudy, with a low around 60. Northeast wind 3 to 7 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tuesday: Scattered showers, mainly after noon. Widespread haze. Mostly sunny, with a high near 79. Calm wind becoming southwest around 5 mph. Chance of precipitation is 30%.

Waimea

Today: Isolated showers, then scattered showers and thunderstorms after noon. Some of the storms could produce heavy rain. Mostly sunny, with a high near 74. Calm wind becoming north 5 to 7 mph in the afternoon. Chance of precipitation is 40%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers, mainly after midnight. Mostly cloudy, with a low around 51. Northeast wind 5 to 10 mph becoming light east after midnight. Chance of precipitation is 40%.

Tuesday: Scattered showers. Partly sunny, with a high near 74. Northeast wind 3 to 7 mph. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Kohala

Today: Isolated showers, then showers likely and possibly a thunderstorm after noon. Some of the storms could produce heavy rain. Partly sunny, with a high near 70. Southwest wind 5 to 11 mph. Chance of precipitation is 60%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely, mainly after midnight. Mostly cloudy, with a low around 44. Light and variable wind. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Showers likely, mainly after noon. Partly sunny, with a high near 70. North wind 3 to 8 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Isolated showers. Mostly sunny, with a high near 79. Southeast wind 5 to 9 mph becoming light in the afternoon. Chance of precipitation is 20%.

Tonight: Isolated showers. Widespread haze after 7pm. Partly cloudy, with a low around 69. Light and variable wind becoming east northeast 5 to 9 mph in the evening. Chance of precipitation is 20%.

Tuesday: Scattered showers, mainly between 7am and 1pm. Widespread haze. Mostly sunny, with a high near 79. East wind 6 to 9 mph. Chance of precipitation is 30%.

Puna

Today: Scattered showers, with thunderstorms also possible after noon. Some of the storms could produce heavy rain. Widespread haze. Partly sunny, with a high near 76. Calm wind becoming west 5 to 9 mph in the morning. Chance of precipitation is 50%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Showers likely, mainly before midnight. Mostly cloudy, with a low around 60. Light and variable wind. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

Tuesday: Scattered showers. Partly sunny, with a high near 76. Light north northeast wind becoming north 8 to 13 mph in the morning. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Waikoloa

Today: Isolated showers, with thunderstorms also possible after noon. Some of the storms could produce heavy rain. Mostly sunny, with a high near 80. Light and variable wind becoming north around 6 mph in the afternoon. Chance of precipitation is 20%.

Tonight: Isolated showers. The rain could be heavy at times. Partly cloudy, with a low around 60. North northeast wind 5 to 9 mph becoming calm after midnight. Chance of precipitation is 20%.

Tuesday: Isolated showers before noon. Sunny, with a high near 80. East northeast wind around 6 mph becoming light and variable. Chance of precipitation is 20%.

Detailed Forecast

Synopsis

The threat for locally heavy rain remains through today as another upper level disturbance approaches the islands from the north. A weakening surface trough near Oahu is expected to move east across Maui County today and the Big Island tonight. Moderate to strong trade winds are expected to expand gradually eastward from Kauai today through Wednesday. Breezy trade winds are on tap for the upcoming weekend with showers favoring the windward and mountain areas.

Discussion

Except for the burst of heavy showers in the Waikoloa area early Sunday evening and the passing showers on Kauai, it has been a rather dry night. A land breeze over the islands from Oahu eastward is keeping the showers from moving onshore. This is particularly evident along the Puna and Kau coast of the Big Island where scattered showers just off the coast have been trying to move onshore. A couple have made in only to fall apart. East Oahu as well has seen a couple of light showers making on shore. The showers over Kauai have been confined to the northern half of the islands. The passing showers have been mostly light with under a tenth of an inch an hour.
Latest radar loop shows a north to south oriented surface trough over Oahu. The trough separates a southerly wind flow to the east of the trough and a northeast flow to the west of the trough. This trough is forecast to weaken as it moves east through Maui County the rest of today, then the Big Island tonight. The light winds from Oahu eastward will promote an onshore sea breeze this morning. With ample moisture, an unstable air mass, and daytime heating, will result in some scattered showers this afternoon, possibly more than yesterday. An upper level disturbance may enhance some of these showers. A thunderstorm or two is possible for the Big Island this afternoon as well. Although the air mass will be more stable from tonight on, there will still be some lingering instability over the Big Island. It won’t be until Thursday where the instability clears out. This leftover instability will favor scattered showers for leeward Big Island each afternoon and early evening through Thursday. Afternoon showers will be less thereafter.
A Flash Flood Watch remains in effect for all islands through late this afternoon. An extension of this watch is possible. If there is one, it is only for tonight.

Aviation

With a nearly stationary surface trough near Oahu, winds will be fairly light east of the trough axis. To the west, conditions will be moderate to locally breezy, from the north and northeast. The surface trough, along with its upper air component, will keep the atmosphere unstable. The chance of showers, some heavy, and accompanying MVFR and isolated IFR restrictions, remains a threat in most areas, as well as isolated thunderstorms over the Big Island this afternoon. Otherwise, VFR will prevail.
AIRMET Sierra remains posted for mountain obscuration over Kauai.

Marine

A surface trough now over Oahu is expected to weaken as it moves eastward the rest of today. It will maintain breezy northeast winds over Kauai western waters, and a light southeast wind flow elsewhere today. With the demise of the surface trough, high pressure building north of the islands will usher in moderate to strong trades across the island chain by midweek. Meanwhile, the potential for heavy showers and thunderstorms remains through today.
The current small craft advisory (SCA) is posted through today for hazardous seas from a large north swell, and a combination of winds and seas in waters west of Kauai. The large north swell will also bring advisory level surf to exposed shores. These areas include the north, east and west facing shores of Kauai County, Molokai and Maui; as well as the north and east facing shores of Oahu and the Big Island. Some near advisory waves will also sneak into the coastline north of Keahole Point on the Big Island, and the north shore of Lanai. This swell will decline Tuesday, but could still be advisory levels along north and east facing shores. A smaller northwest swell is possible Wednesday and Thursday. Trade wind swell will increase over the second half of the week. Surf along east facing shores will likely remain above advisory levels as winds strengthen.

HFO Watches/Warnings/Advisories

Flash Flood Watch through this afternoon for all Hawaii islands.
High Surf Advisory until 6 PM HST this evening 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.
Small Craft Advisory until 6 PM HST this evening 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