Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny with isolated showers. Highs around 81 near the shore to around 71 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows 66 to 71 near the shore to around 57 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny with isolated showers. Highs around 82 near the shore to around 71 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 78 to 84. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 66 to 71. Northeast winds around 15 mph. Chance of rain 70 percent.

Tuesday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 78 to 83. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Breezy. Mostly cloudy with showers likely. Highs 70 to 77 in the valleys to around 64 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers. Lows around 61 in the valleys to around 54 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Tuesday: Mostly cloudy. Showers in the morning, then showers likely in the afternoon. Highs 69 to 76 in the valleys to around 64 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 72 to 81. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Showers likely in the evening, then showers after midnight. Lows 61 to 69. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Tuesday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 71 to 80. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 71 to 82. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Cloudy with showers. Lows 59 to 71. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Tuesday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 71 to 81. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will prevail into next weekend, except for a period of slightly lighter winds around the middle of the week. Strong trade winds are possible next weekend. Showery low clouds will favor windward slopes and coasts, with some showers occasionally drifting into leeward areas of the smaller islands. The island atmosphere will be somewhat unstable the next couple of days, allowing some showers to become briefly heavy.

Discussion

Surface high pressure to the distant NW will move E into tomorrow, then move S and weaken tomorrow night and Wednesday. The high center is then expected to re-organize to the distant NE of the islands on Thursday, then strengthen while moving to a position N of the islands by next weekend. As a result, moderate to locally breezy ENE trade winds will persist into tomorrow, then diminish slightly around mid-week. Winds will strengthen toward the end of the week, with the potential to become strong by next weekend as a deep-layer ridge builds N of the islands.
An ENE-WSW oriented moisture axis (marked by showery unstable cumulus) just N and NE of the islands is being supported by weakly convergent NE flow. The bulk of this moisture remains just N of Kauai this morning. Randomly distributed, relatively small open- celled cumulus elements arriving on the trade flow have been efficiently creating showers overnight- mainly over windward areas, but radar shows a few light showers spreading to leeward areas. Morning soundings indicate an elevated subsidence inversion near 10kft, with PWAT near 1.1″.
Although guidance differs on the details, the general expectation is that the moisture axis to the N and NE will slide S and SW over the islands as the high builds E, fueling periods of showers over windward areas, and an abundance of daytime rainbows, as leeward areas remain partly to mostly sunny. Current forecast anticipates increasing rainfall chances over Kauai later today, shifting to Oahu and Maui County (and possibly Big Island) tonight and tomorrow.
Water vapor imagery shows a developing trough aloft N of the islands (near 29N 160W), and guidance indicates it will pass near and NE of the islands tonight and Tuesday. Latest HREF probabilities of 1-hour PoP > 0.50″ support the notion that some briefly heavy downpours may develop as the trough enhances the incoming moisture, mainly tonight. With trade winds remaining in place and moisture somewhat limited, showers are not expected to linger over any one area sufficiently long to pose a significant flood threat, but localized ponding of water from brief downpours is possible. After a brief period of modest stabilization Wednesday and Thursday, another passing trough aloft could enhance incoming moisture again toward the end of the week.

Aviation

Unstable low clouds northeast of the Hawaiian Islands are drifting in on the trade winds producing periods of showers along windward and mountain areas through the early morning hours. Brief periods of MVFR conditions are possible over windward locations. Moderate to locally breezy trade winds will prevail through this afternoon. Wind speeds will then decrease to more moderate levels on Tuesday.
AIRMET Tango for moderate turbulence over and immediately south through west of mountains remains in effect for all islands.

Marine

Surface high pressure will exist north of the state in some form over the next week, maintaining trade winds through this week. Winds speeds and the northwest swell have dropped enough to scale back the Small Craft Advisory (SCA) to the typical waters around Maui County and the Big Island through tonight. Moderate to locally fresh northeast trade winds will continue through tonight then weaken a bit and shift to a more typical east-northeast direction around mid- week. Much stronger trades are possible next weekend as a strong surface high sets up far northeast of the area.
The current long-period northwest (320 deg) swell is now on the decline and will continue to lower today. The High Surf Advisory (HSA) for north and west facing shores of Niihau and Kauai, as well as north facing shores of Oahu, Molokai, and Maui has been cancelled. The next northwest swell is scheduled to arrive Tuesday with a similar size, so advisory conditions are possible again along many north and west-facing exposures late Tuesday into Wednesday. This swell will be reinforced by a more northerly swell late Wednesday into Thursday.
The trade winds over and upstream of the islands are generating choppy, rough seas along east-facing shores, but will decline through the middle of the week as winds briefly taper off. A small south swell is possible during the second half of this week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Tuesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov