Hilo

Tonight: Cloudy with scattered showers. Lows 62 to 70 near the shore to 52 to 57 at 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Cloudy with numerous showers. Highs 75 to 80 near the shore to around 62 at 4000 feet. North winds up to 10 mph. Chance of rain 70 percent.

Tuesday Night: Cloudy with occasional showers. Lows 60 to 69 near the shore to 52 to 59 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 90 percent.

Kona

Tonight: Cloudy with scattered showers. Lows 69 to 75 near the shore to around 52 near 5000 feet. Light winds. Chance of rain 50 percent.

Tuesday: Cloudy. Scattered showers early in the morning, then numerous showers in the late morning and afternoon. Highs 80 to 86 near the shore to around 64 near 5000 feet. Light winds. Chance of rain 70 percent.

Tuesday Night: Cloudy with scattered showers. Lows 69 to 74 near the shore to around 52 near 5000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 50 percent.

Waimea

Tonight: Cloudy with scattered showers. Lows 62 to 72 near the shore to 56 to 63 near 3000 feet. East winds up to 15 mph in the evening becoming light. Chance of rain 40 percent.

Tuesday: Cloudy with scattered showers. Highs around 77 near the shore to 64 to 75 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Cloudy and breezy. Occasional showers in the evening, then numerous showers after midnight. Lows 61 to 70 near the shore to 55 to 63 near 3000 feet. East winds up to 20 mph. Chance of rain 90 percent.

Kohala

Tonight: Cloudy with scattered showers. Lows 62 to 72 near the shore to 56 to 63 near 3000 feet. East winds up to 15 mph in the evening becoming light. Chance of rain 40 percent.

Tuesday: Cloudy with scattered showers. Highs around 77 near the shore to 64 to 75 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Cloudy and breezy. Occasional showers in the evening, then numerous showers after midnight. Lows 61 to 70 near the shore to 55 to 63 near 3000 feet. East winds up to 20 mph. Chance of rain 90 percent.

South Big Island

Tonight: Breezy. Cloudy with scattered showers. Lows around 73 near the shore to around 55 near 5000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

Tuesday: Cloudy. Scattered showers early in the morning, then numerous showers in the late morning and afternoon. Highs around 82 near the shore to around 63 near 5000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Tuesday Night: Cloudy and breezy. Occasional showers in the evening, then scattered showers after midnight. Lows around 73 near the shore to around 55 near 5000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Puna

Tonight: Cloudy with scattered showers. Lows 62 to 70 near the shore to 52 to 57 at 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Cloudy with numerous showers. Highs 75 to 80 near the shore to around 62 at 4000 feet. North winds up to 10 mph. Chance of rain 70 percent.

Tuesday Night: Cloudy with occasional showers. Lows 60 to 69 near the shore to 52 to 59 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 90 percent.

Waikoloa

Tonight: Cloudy with isolated showers. Lows around 74 near the shore to 51 to 56 above 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Tuesday: Cloudy with scattered showers. Highs around 83 near the shore to 62 to 67 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tuesday Night: Cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 73 near the shore to around 54 above 4000 feet. Light winds becoming east up to 10 mph after midnight. Chance of rain 50 percent.

Detailed Forecast

Synopsis

An upper level low southwest of the islands will pull moisture over the eastern half of the state through Tuesday. This feature, along with a developing surface trough, will bring an increased chance of heavier showers Tuesday night through Wednesday, especially for windward portions of Maui and the Big Island. The chance of heavy rainfall diminishes late Wednesday into Thursday, though breezy showery trades will persist. A brief period of stable and drier trade wind conditions is expected on Friday, followed by more showery weather into the weekend as a cold front advances toward the island chain.

Discussion

Latest water vapor imagery depicts an upper level low centered several hundred miles south southwest of the state with an associated cyclonic spin aloft over the island chain. Enhanced mid and upper level moisture, driven by the low, can be seen streaming in from the southwest over Maui County and the Big Island. Near the surface, moderate easterly trades continue to push typical light to moderate showers against windward and mauka areas. This pattern is expected to hold into the early evening.
By late evening and into tonight, the mid and upper level cloud shield is progged to thicken, especially over the eastern portion of the state. Hi- res model guidance, such as the WRFARW and FV3, show stratiform precipitation developing over the summits first, then possibly spreading to lower elevations as the dry air below slowly beings to moisten. Freezing levels near 13Kft or 14Kft, along relatively dry air in place nearly the surface, should support a wintry mix of rain and snow at summits of the Mauna Loa and Mauna Kea on the Big Island. Thus, have opted to issue a Winter Weather Advisory from 6 PM HST this evening through the day Tuesday.
By Tuesday, both the GFS and ECMWF begin to deepen an upper level trough northwest of the state as a surface trough develops south of the Big Island. As conditions become more unstable aloft, both models indicate an area of rather heavy rainfall developing south of the Big Island, in association with the aforementioned surface trough. However, uncertainly remains an issue. The GFS is still much more robust with the intensity than the ECWMF, though it has been trending slightly weaker with the latest 18Z run. This pocket of deep moisture should lift northward late Tuesday into Wednesday, causing conditions to deteriorate for windward portions of the Big Island and Maui. Strong trades, combined with deep moisture and some instability aloft, may lead to a periods of heavy rainfall for these areas and a Flood Watch may be needed late Tuesday night through Wednesday. If current trends hold, however, flooding will be limited to mainly the nuisance variety and the Watch wouldn't be necessary. Forecast rainfall totals currently range from under an inch with the ECMWF's weaker forcing to one to two inches from the GFS. For all other islands Tuesday night through Wednesday, the inversion height should deepen to near 15000 feet. Surface high pressure building far north of the state will bring gradient driven strong trades with scattered to numerous showers that will affect both windward and leeward sides of the islands. The flooding threat remains low over the smaller islands due to the speedy nature of the showers and lack of any substantial forcing.
Any threat for heavy rainfall will decrease late Wednesday, but breezy and wet conditions are expected into Thursday. The strong surface high passing to the north will maintain breezy trade winds, and even though precipitable water will be decreasing, the GFS and ECMWF keep abundant moisture around the islands, suggesting a rather wet pattern.
A brief period of stable and drier trade wind conditions is expected on Friday, followed by more showery weather into the weekend as a cold front approaches the island chain.

Aviation

Moderate east southeast winds will gradually weaken overnight, with land breezes possible across the western end of the state. In this flow, isolated to scattered showers will move into windward areas, with some weak surface convergence boundaries downstream of island terrain bringing a few showers to leeward areas at times. VFR conditions will generally prevail, with brief MVFR possible in showers.
On Tuesday, winds will strengthen and back out of the east northeast, focusing low clouds and showers over windward areas. However, winds will remain lighter and veered east-southeast across the eastern end of the state. As deeper moisture streams up from the southeast, showers will increase in coverage beginning early Tuesday morning. MVFR, or even IFR, conditions will be possible in heavier showers.
AIRMET Sierra is in effect for mountain obscuration for windward portions of Maui and the Big Island this afternoon. This AIRMET will likely be needed for portions of the island chain through at least Tuesday.
AIRMET Tango is in effect for moderate turbulence in the mid to upper levels. This AIRMET will likely be needed through at least Tuesday morning.
AIRMET Zulu is in effect for some light icing due to the influx of high clouds and will likely be needed into Tuesday morning.

Marine

A front approaching the state from the far northwest will weaken the ridge and veer moderate to locally fresh easterly trade winds more to a east southeast direction to more gentle to moderate speeds the tonight into Tuesday. The front will weaken as it enters the northwest offshore waters Tuesday, then lift to the north Tuesday night into Wednesday. Near gale- force winds are possible behind the front in the offshore waters. An upper level trough and deep moisture surging from the south could produce thunderstorms over the offshore waters. The confidence of thunderstorms over the coastal waters has decreased thus have removed them from the forecast at this time but will continue to monitor.
Behind the front, a new high building north of the islands will help trades strengthen across the state to fresh to locally near gale speeds. Combined with incoming northwesterly swells, expect winds and seas to exceed Small Craft Advisory thresholds for exposed coastal waters Wednesday into Thursday.
A small, short period NE and small, medium period NW swell will continue to slowly decline into Tuesday. Overlapping NW to NNW swells rest of this week will keep surf heights boosted along exposed N and W facing shores. A pair of small to moderate, long period NNW (310-340 degree) swells will arrive Tuesday, peaking Wednesday. Surf could peak near or above High Surf Advisory (HSA) thresholds along exposed N and W facing shores before gradually declining Wednesday night through the end of the week. Another overlapping small, short to medium period N (350-010 degree) swell arrives from Thursday into Friday. Then another moderate, long period NW (310-330 degree) swell arrives Friday, peaking near HSA thresholds over the weekend.
Surf along E facing shores will continue to decline tonight into Tuesday due to the weakening of the local and upstream trade winds. As a new high pressure builds N of the state Wednesday through Thursday, rough and choppy surf along E shores could near HSA levels. For S shores, periods of tiny background south swell energy will continue to move through keeping surf from going flat.

Fire weather

Moderate trades and higher humidity will maintain conditions below critical fire weather thresholds. Wet conditions are expected Tuesday into Thursday, with heavy rainfall possible over recent burn areas on the Big Island.

HFO Watches/Warnings/Advisories

Winter Weather Advisory until 6 PM HST Tuesday for Big Island Summits.

Data Courtesy of NOAA.gov