West Side

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South Side

Today: Sunny. Highs around 84. East winds 10 to 15 mph shifting to the southeast in the afternoon.

Tonight: Mostly clear. Lows 62 to 72. Northeast winds 10 to 15 mph.

Saturday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Haze in the afternoon. Highs around 83. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

North Shore

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 80 near the shore to around 63 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 66 near the shore to around 48 near 5000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 78 near the shore to around 64 near 5000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Central Maui

Today: Sunny and breezy. Highs 79 to 85. East winds 10 to 20 mph.

Tonight: Mostly clear. Breezy. Isolated showers after midnight. Lows around 64. East winds 10 to 20 mph. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 78 to 84. East winds 10 to 15 mph. Chance of rain 40 percent.

Upcountry

Today: Sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs around 61 at the visitor center to around 59 at the summit. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Haze in the evening. Partly cloudy with scattered showers. Lows around 43 at the visitor center to around 37 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Haze through the day. Highs 53 to 65. East winds around 10 mph. Chance of rain 50 percent.

East Maui

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 80 near the shore to around 63 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 66 near the shore to around 48 near 5000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs around 78 near the shore to around 64 near 5000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Lanai City

Today: Sunny. Isolated showers in the afternoon. Highs 71 to 79. North winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 62. Northeast winds 10 to 15 mph.

Saturday: Mostly sunny. Isolated showers in the afternoon. Highs 70 to 78. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaunakakai

Today: Sunny and breezy. Isolated showers in the afternoon. Highs 67 to 83. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening, then scattered showers after midnight. Lows 53 to 70. East winds 10 to 15 mph. Chance of rain 40 percent.

Saturday: Haze in the morning. Mostly sunny with isolated showers. Highs 67 to 83. East winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy and gusty trade winds will gradually decline today as a surface high pressure to the northeast slowly weakens. Showers will remain focused over windward areas, with some afternoon showers developing across the leeward Big island slopes. East to southeast trades will be light enough for afternoon sea breezes and spotty showers to develop over all leeward areas Saturday into early next week. A upper level disturbance will bring some instability, resulting in some briefly heavier showers.

Discussion

Although the general forecast philosophy hasn't changed, there were some changes to the forecast with the morning package. The PoPs over the windward sections of the islands were nudged upwards tonight (Friday night) in line with the National Blend of Models which factors in the higher resolution models. A more noticeable increase to the PoPs is noted Saturday night into Monday. The PoPs were increased over much of the coastal waters, and the windward areas, with little change in the PoPs over leeward areas. Main reasoning for that increase was the general consensus across the models.
A 1029 mb high remains to the northeast of the islands, and has shifted just a bit to the east over the last several hours. We are starting to see winds turn more to the east and southeast as a result. Satellite imagery overnight show low clouds to the east of Kauai moving in from the east-southeast while clouds to the east of the Big Island remain more easterly. Expect winds over the islands to be on a downward trend, particularly this afternoon and tonight as a result. Showers will continue to be carried in on the easterly winds, and remain focused over the windward slopes of most islands.
More instability is expected to develop over the islands late tonight and into Saturday, which coupled with the surface high weakening will help to weaken the trades over the region. Additionally, a surface low pressure system is expected to develop about 700 miles northwest of Kauai, which will help to turn the winds to the east and southeast.
An upper level trough already exists about 1000 miles to the northwest of Kauai, and it is from this system that the surface low is expected to form. The upper level trough is expected to remain to the west of the surface feature, but 500 mb heights near the islands will fall as a weak subtropical jet creeps toward the islands. This will result in the developing instability as early as Friday night that will wipe over the inversion and could lead to an increase in shower activity. Rainfall would continue to favor the east and windward slopes, but with the weaker winds, there could be the development of afternoon and evening showers over leeward areas. The global models keep the highest instability just north of the islands, so will need to continue to monitor their handling of this over the next several model runs.
The GFS, ECMWF and the National Blend of Models are in good agreement with the possibility of thunderstorms just north of the islands Saturday night through Sunday night. There is still some uncertainty with placement, and since most of the areas would be off land, have held off on putting it into the forecast grids at this time as we monitor future model runs.
A brief increase in trade winds is possible Sunday as the surface low weakens. The GFS weakens the low faster than the ECMWF, so will have to watch future runs to see which ends up happening. In either event, additional unstable light to moderate east to east- southeast winds are expected early next week. Persistent upper- level troughing over the region will keep the atmosphere slightly unstable, while surface troughing to the northwest will favor weakened and veered winds Sunday night into Tuesday. The GFS and ECMWF are showing the highest chances for rainfall just north of the island chain during this time, but there will be a chance of heavy showers over windward slopes, with spotty afternoon showers leeward.
A return to a more stable trade wind flow is expected by Wednesday.

Aviation

Breezy to locally strong trade winds will continue this morning before gradually weakening through Saturday. Scattered showers, located mainly along windward areas this morning, may bring brief periods of MVFR ceilings and visibility. By this afternoon, isolated showers may also develop over portions of leeward Kauai, Oahu, and west Maui. Otherwise, VFR conditions are generally expected elsewhere.
AIRMET Tango remains in effect through at least the remainder of this morning for moderate low level turbulence over and downwind of island terrain. Tango will likely be dropped by tonight as the flow weakens.

Marine

Surface high pressure about 660 nm northeast of Oahu will continue to drift east and weaken over the next couple of days. Fresh to locally strong trades will ease to moderate to locally fresh speeds by early evening and hold through through Saturday. The Small Craft Advisory (SCA) has been trimmed back to windward waters east of the Kaiwi Channel, excluding Maalaea Bay and Leeward Maui through this afternoon and should drop below advisory by this evening. Another strong high will pass north of the state Sunday into early next week as a strong low develops northwest of the state. This may strengthen trades to moderate to locally strong speeds briefly Sunday, returning typically SCA conditions to windier waters. The low is expected to shift slightly east towards the state Monday before stalling Tuesday and weakening. This could veer winds out of the east- southeast and winds and ease wind speeds to light and variable over the western half of the state and moderate to locally fresh over the eastern half of the state. Moderate to locally strong trades is expected to gradually return during the second half of next week as another strong high builds northeast of the state and the remnant low/trough dissipates far northwest.
Forerunners of a new small to moderate, long period west northwest (300-320 degree) swell have reached the Kauai near shore buoy. This swell will fill in throughout the day before peaking below advisory levels this afternoon into early evening. This swell will gradually fade over the weekend. A moderate, medium period north northwest swell (340-350) may overlap the fading west northwest swell Sunday night into Monday. In the long range, a series of small, long period northwest swell look to keep surf elevated through much of next week.
Surf along east-facing shores will remain rough and choppy but may ease a couple of notches later today and Saturday, and then again early next week as winds fluctuate in strength.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov