Photo Credit: Tyler Rooke

West Side

Washington’s Birthday: Isolated showers after noon. Mostly sunny, with a high near 85. Light and variable wind. Chance of precipitation is 20%.

Tonight: Isolated showers after midnight. Partly cloudy, with a low around 66. Calm wind. Chance of precipitation is 20%.

Tuesday: Isolated showers and thunderstorms after noon. Mostly sunny, with a high near 84. Calm wind becoming west around 5 mph. Chance of precipitation is 20%.

South Side

Washington’s Birthday: Scattered showers after noon. Mostly sunny, with a high near 85. Calm wind becoming west southwest around 5 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 64. Calm wind. Chance of precipitation is 20%.

Tuesday: Mostly sunny, with a high near 84. Calm wind becoming west around 6 mph.

North Shore

Washington’s Birthday: Scattered showers, mainly after 1pm. Mostly sunny, with a high near 83. Light and variable wind becoming north 5 to 7 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers, mainly before 7pm. Partly cloudy, with a low around 65. East northeast wind around 5 mph becoming calm in the evening. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Isolated showers before 7am, then scattered showers and thunderstorms after 1pm. Mostly sunny, with a high near 82. Light southeast wind becoming east 6 to 11 mph 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.

Central Maui

Washington’s Birthday: Scattered showers, mainly after noon. Mostly sunny, with a high near 83. Calm wind becoming east northeast 5 to 7 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Isolated showers after midnight. Partly cloudy, with a low around 63. Calm wind. Chance of precipitation is 20%.

Tuesday: Isolated showers and thunderstorms after noon. Mostly sunny, with a high near 82. Calm wind becoming east northeast 5 to 8 mph. Chance of precipitation is 20%.

Upcountry

Washington’s Birthday: Scattered showers after noon. Mostly sunny, with a high near 70. Calm wind becoming west around 6 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 53. West northwest wind around 5 mph becoming calm in the evening. Chance of precipitation is 20%.

Tuesday: Mostly sunny, with a high near 70. Calm wind becoming west northwest 5 to 7 mph in the afternoon.

East Maui

Washington’s Birthday: Scattered showers. Partly sunny, with a high near 81. Light south southeast wind becoming east 5 to 10 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 61. East southeast wind 7 to 10 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tuesday: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 80. Southeast wind 7 to 10 mph. Chance of precipitation is 50%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Lanai City

Washington’s Birthday: Scattered showers after noon. Mostly sunny, with a high near 72. Southwest wind 5 to 8 mph becoming calm in the afternoon. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 64. Calm wind. Chance of precipitation is 20%.

Tuesday: Isolated showers and thunderstorms after noon. Mostly sunny, with a high near 73. West wind around 6 mph becoming calm in the afternoon. Chance of precipitation is 20%.

Kaunakakai

Washington’s Birthday: Scattered showers, mainly after noon. Mostly sunny, with a high near 82. West southwest wind 5 to 8 mph becoming calm in the afternoon. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 69. Calm wind. Chance of precipitation is 20%.

Tuesday: Mostly sunny, with a high near 81. Light and variable wind.

Detailed Forecast

Synopsis

An upper level low south of the Big Island will slowly drift west today. Northwest of the islands a cold front will approach and stall near Kauai late Tuesday into Wednesday. Expect a southeast wind pattern to continue for the Big Island today with land and sea breezes over the smaller islands. Clouds and showers will build over island mountain and interior sections. On Tuesday, light winds begin to change back to easterly trade winds as the cold front approaches Kauai. Prefrontal shower bands will produce widespread rain over Kauai County with locally heavy rainfall at times and isolated thunderstorms. The front will stall near Kauai late Tuesday into Wednesday with wet weather forecast over the western islands. Unsettled moderate to breezy trade winds will remain in the forecast across the state from Wednesday onward with higher rainfall chances favoring windward and mountain areas.

Discussion

Satellite imagery this morning continues to show an upper level low a few hundred miles south of the Big Island. This low will drift westward just south of Kauai by Tuesday. The high pressure ridge north of the state will remain weak due to the upper low, and the cold front approaching the islands from the northwest. Wind directions will remain in a southeasterly wind pattern today. Wind shadowing for the smaller islands northwest of the the Big Island will keep local scale land and sea breezes in the short range forecast over the smaller islands today. The upper level low will keep deep and unstable moisture over the region ahead of the approaching front. Converging sea breezes over each island will build clouds over island mountain and interior sections today. Enough unstable moisture and sea breeze convergence may produce a few thunderstorms over island interiors in the afternoon to early evening hours. Shower trends will increase from the mid afternoon through the early evening hours as these clouds start to lose vertical development.
On Tuesday, the weather pattern changes yet again. Trade winds will begin to return as a high pressure system builds in north of the island chain. Shower activity will increase along trade wind and sea breeze convergence zones, and along windward mountain slopes. A cold front will approach Kauai and Niihau from the northwest, increasing shower trends over the western islands. The upper low and unstable moisture lingering south of Kauai will be drawn northward ahead of the front. Short range global model solutions are showing prefrontal shower bands forming over Kauai County from Tuesday afternoon through Wednesday morning.
Rainfall Impacts…Widespread rain will develop over Niihau and Kauai, with locally heavy showers and a few thunderstorms are forecast mainly on Tuesday and Wednesday. For now it remains too early to consider a Flash Flood Watch for Kauai County. Our main concern with this developing weather event is in how close the stalling front gets to the islands in Kauai County. Forecast precipitation amounts will depend heavily on the final position of this frontal cloud band. Higher amounts of rainfall could develop if the front stalls over these islands potentially leading to a Flash Flood Watch situation. Forecaster confidence with rainfall amounts for the western islands is moderate, as a very small difference in the location of this stalled front will make a large difference in the amount of rainfall for Kauai County over the next few days.
Wednesday through Saturday…Moderate trade winds return to the region by Wednesday as a high pressure system builds in far north of the Hawaiian Islands. Lingering unstable moisture over Kauai County will keep enhanced shower activity with locally heavy rain and isolated thunderstorms in the forecast at least through Wednesday afternoon. Global models suggest heavy shower activity decreasing by Thursday as the low level easterly trade winds drive the diminishing frontal cloud band westward away from the state. However, a lingering upper level trough pattern over the region will keep unsettled trade wind showers in the forecast through Saturday with cloud heights around the 10,000 foot level. Expect moderate to breezy trade winds to continue into the weekend. Passing showers will affect all islands, favoring windward and mountain areas.
Global weather models are in good agreement with the short range wet weather forecast through Wednesday. The challenge with this forecast continues to be how far east the frontal shower band will progress before stalling out, and in how much rain the small scale prefrontal convergence bands will add the the precipitation totals over Kauai and Oahu ahead of the frontal zone. Chances for Flash Flooding over Kauai and Niihau remain elevated, however it remains too early to issue any products with this evolving weather pattern. A Flash Flood Watch may be issued for this event later today or tonight. Stay tuned.

Aviation

An upper-level low meandering south of the Big Island is causing some atmospheric instability over portions of Hawaii, especially in the vicinity of the eastern islands. Elsewhere, a cold front located northwest of Kauai is causing weak low-level background flow from the southeast over the state early this morning. As a result alternating local nighttime land breezes and afternoon sea breezes are occurring over each of the islands. Overall, VFR conditions will continue to prevail across most areas through tonight. However, expect pockets of MVFR conditions over parts of the state, such as the south through east facing slopes of the islands. Once sea breezes form later today, MVFR conditions might develop over leeward and interior sections of some of the islands, especially the leeward Big Island.
Strong upper-level winds associated with the low aloft are over the eastern end of the state. These strong winds are likely producing moderate turbulence aloft, so AIRMET Tango is currently in effect for the layer between 25,000 and 40,000 feet covering the Big Island and Maui. This turbulence is expected to continue through late this morning.
AIRMET Sierra may be required later today for some sections of the state if widespread low clouds and showers develop over the higher terrain once the sea breezes become established.

Marine

High pressure will remain nearly stationary northeast of the islands through Tuesday, as a cold front approaches from the northwest. This will keep moderate to fresh southeast winds in place over the eastern islands, with lighter winds over the western end of the state. The cold front is expected to stall near Kauai Tuesday night through Thursday while high pressure builds to the northeast and northwest of the state. This will bring a return of trade winds to the island chain Tuesday night and Wednesday, with the trades ramping up to fresh to strong levels Thursday through the weekend. Unsettled weather including thunderstorms will be possible near the front Tuesday through Wednesday.
A Small Craft Advisory (SCA) remains in effect for most windward waters today due to elevated seas. Seas are expected to drop below advisory thresholds by late this afternoon. SCA’s may be needed once again for portions of the marine area due to winds/seas or a combination of the two Wednesday through the weekend.
The NOAA buoys northwest of Hawaii have held fairly steady overnight, although the main swell direction has shifted to the west-northwest. As a result, the core of the swell energy will be focused toward north and west facing shores of Niihau, Kauai, and west facing shores of the Big Island, and High Surf Advisories remain in effect for these areas. The change in direction will keep surf just below advisory levels along north and west facing shores of Oahu, Molokai and north facing shores of Maui, so the High Surf Advisory for these areas has been cancelled. This swell is expected to slowly lower today through Tuesday, and the expectation is that surf will fall below advisory levels along north and west facing shores of Niihau and Kauai by late this afternoon. Surf is expected to hold at advisory levels along west facing shores of the Big Island tonight however, and may remain in advisory territory into Tuesday. As this swell continues to decline Tuesday night, a new moderate northwest swell is expected to build, peak Wednesday through Thursday, then decline through the weekend. A new small west-northwest swell may move through over the weekend.
Surf along east facing shores will trend slightly lower through mid week. East shore surf should then ramp up late in the week as trade winds increase over and upstream of the islands, possibly approaching advisory levels late in the weekend. Surf along south facing shores will remain small through the week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Niihau, Kauai Windward, Kauai Leeward.
High Surf Advisory until 6 AM HST Tuesday for Kona, Kohala.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters.

Data Courtesy of NOAA.gov