Photo Credit: Tyler Rooke

West Side

Today: Isolated showers and thunderstorms after 1pm. Mostly sunny, with a high near 83. Light southeast wind. Chance of precipitation is 20%.

Tonight: Isolated showers and thunderstorms. Partly cloudy, with a low around 66. Calm wind becoming east northeast 5 to 7 mph after midnight. Chance of precipitation is 20%.

Wednesday: Isolated showers. Partly sunny, with a high near 83. East wind around 5 mph becoming calm in the afternoon. Chance of precipitation is 20%.

South Side

Today: Mostly sunny, with a high near 83. East wind around 6 mph becoming calm in the morning.

Tonight: Isolated showers after midnight. Partly cloudy, with a low around 64. East northeast wind around 6 mph becoming calm after midnight. Chance of precipitation is 20%.

Wednesday: Isolated showers. Partly sunny, with a high near 83. Calm wind becoming northeast 5 to 8 mph in the afternoon. Chance of precipitation is 20%.

North Shore

Today: Isolated showers and thunderstorms after 1pm. Mostly sunny, with a high near 81. East wind 6 to 13 mph. Chance of precipitation is 20%.

Tonight: Isolated showers and thunderstorms. Partly cloudy, with a low around 65. East wind 6 to 10 mph. Chance of precipitation is 20%.

Wednesday: Scattered showers, mainly after 7am. Mostly cloudy, with a high near 81. East wind 11 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Central Maui

Today: Isolated showers and thunderstorms after 1pm. Mostly sunny, with a high near 81. Calm wind becoming east northeast 5 to 8 mph in the afternoon. Chance of precipitation is 20%.

Tonight: Isolated showers and thunderstorms, then scattered showers after 7pm. Mostly cloudy, with a low around 63. Calm wind becoming northeast 5 to 7 mph after midnight. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Wednesday: Scattered showers. Mostly cloudy, with a high near 81. North northeast wind 6 to 8 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Upcountry

Today: Isolated showers and thunderstorms after noon. Mostly sunny, with a high near 69. East wind around 6 mph becoming light and variable. Chance of precipitation is 20%.

Tonight: Partly cloudy, with a low around 53. East wind around 6 mph becoming light and variable after midnight.

Wednesday: Partly sunny, with a high near 68. Light and variable wind becoming east 5 to 10 mph in the afternoon.

East Maui

Today: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 79. Southeast wind 10 to 13 mph. Chance of precipitation is 40%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely, mainly after midnight. Mostly cloudy, with a low around 61. Southeast wind 7 to 11 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Wednesday: Scattered showers. Mostly cloudy, with a high near 79. Southeast wind 7 to 10 mph. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Lanai City

Today: Isolated showers and thunderstorms after noon. Mostly sunny, with a high near 73. Calm wind becoming south southeast around 5 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Mostly cloudy, with a low around 65. Light and variable wind becoming north 5 to 7 mph after midnight. Chance of precipitation is 20%.

Wednesday: Isolated showers. Partly sunny, with a high near 73. Light and variable wind becoming east northeast 6 to 11 mph in the afternoon. Chance of precipitation is 20%.

Kaunakakai

Today: Isolated showers and thunderstorms after noon. Mostly sunny, with a high near 81. Calm wind becoming south southeast around 6 mph. Chance of precipitation is 20%.

Tonight: Scattered showers, mainly before midnight. Mostly cloudy, with a low around 69. Calm wind becoming east 5 to 9 mph after midnight. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday: Isolated showers. Partly sunny, with a high near 80. Breezy, with an east wind 7 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 20%.

Detailed Forecast

Synopsis

A cold front will stall near Kauai later tonight through Wednesday producing showers across the western islands, with periods of heavy rain and isolated thunderstorms over Kauai County. Large scale southeasterly winds will keep local scale land and sea breezes in the forecast over the smaller islands today. High pressure building in north of the state will allow moderate to breezy trade winds to return from Wednesday on into the weekend. Returning trade winds will push the frontal cloud band westward away from the islands on Thursday. Unstable conditions aloft and a high pressure ridge north of the state will keep moderate to breezy wet trade winds in the forecast through the weekend.

Discussion

The satellite imagery this morning shows an upper level low south of the Hawaiian Islands drifting slowly westward. A cold front, roughly 350 miles northwest of Kauai, will slow as it approaches the western islands. Unstable moisture over the western half of the state is enhancing shower activity for Niihau, Kauai and Oahu. Radar imagery this morning already shows unstable shower bands moving from south to north over Niihau and Kauai producing up to 1 inch per hour of rainfall. The cold front will stall near Kauai later tonight through Wednesday, as the weak upper low will be drawn northward over the western islands. Both systems will combine forces to increase shower trends over the western half of the state through Thursday.
Large scale southeasterly winds will keep the smaller islands (northwest of the Big Island) in a wind shadow, allowing local scale land and sea breezes to continue into Wednesday morning. Unstable moisture over the western islands will keep wet weather in the forecast from Kauai to Oahu. Southerly to southwesterly steering winds aloft, at the 700 mb level, will tend to drive developing shower bands from south to north over these islands today. Shower activity over Kauai and Niihau will increase with locally heavy showers and isolated thunderstorms as the cold front approaches both islands. Flooding concerns for Kauai County will increase from tonight into Wednesday, however forecast confidence is not yet high enough for the issuance of a Flash Flood Watch at this time.
The eastern islands will remain under a drier weather pattern with scattered showers favoring eastern slopes. The exception to this drier pattern will occur along the east to southeast slopes of the Big Island, where large scale southeasterly winds will continue to push shower bands up the mountain slopes enhancing rainfall activity from the Ka’u to Puna to Hilo districts.
By Wednesday, a high pressure system moving from west to east far north of the state will build the ridge north of the islands, allowing moderate trade winds to return. The weakening cold front will stall near Kauai with showers continuing to develop over the Garden Isle through the evening hours. Northeasterly trade winds will push showers up the north and east slopes of Kauai. Showers will become heavy at times with isolated thunderstorms in the forecast. Oahu will also see increasing shower activity as prefrontal shower bands develop and move over both islands. Shower activity for the island in Maui and Hawaii Counties will turn to a more typical wet trade wind weather pattern with enhanced showers forecast along windward and mountain slopes in a fairly unstable environment.
Thursday through Sunday…Trade winds will help to push the weakening frontal zone westward away from the islands on Thursday. Unsettled trade wind weather continues with wind speeds in the moderate to breezy range through the weekend. Shower activity will trend higher over windward and mountain areas, with isolated to scattered showers over leeward areas.

Aviation

Moderate to locally heavy showers have impacted Kauai, particularly the western slopes, for most of night thus far. Although recent radar trends indicate diminishing intensity, occasional showers and MVFR/local IFR will likely continue into the early morning. Diurnal heating and sea breeze convergence will will support deep inland convection, including a chance for thunder, over all of the islands this afternoon. Meanwhile, the cold front approaching from the west will usher in a greater threat for more widespread heavy rain and t-storms, mainly over Kauai and adj waters, by tonight. Winds will remain south to southeasterly in advance of the front.

Marine

High pressure will remain nearly stationary northeast of the islands today, as a cold front approaches from the northwest. This will keep moderate to fresh east to 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 tonight through Thursday while high pressure builds eastward far to the north of the state. This will bring a return of trade winds to the island chain tonight and Wednesday, with the trades ramping up to fresh to strong levels Friday through the weekend. Small Craft Advisories may be needed for portions of the marine area due to winds/seas or a combination of the two Wednesday through the weekend.
Unsettled weather including thunderstorms will be possible across portions of the waters, particularly over the western end of the state through Thursday.
The current west-northwest swell is expected to slowly lower today. The swell will take a bit longer to fade over the eastern end of the state however, and as a result the High Surf Advisory has been extended until 6 PM this evening for west facing shores of the Big Island. This swell will continue to decline tonight, but will be quickly followed by a new moderate northwest swell, which will peak Wednesday through Thursday, then decline through the weekend. A new small west-northwest swell is forecast to move through over the weekend into early next week.
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 reaching advisory levels this weekend into early next week. Surf along south facing shores will remain small through early next week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Kona, Kohala.

Data Courtesy of NOAA.gov