Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Tuesday 30 August 2016

Warnings
Chance for fog/high humidity
Winds may begin to increase

Cloud Cover and Precipitation Forecast
There is a risk for fog, high humidity and perhaps summit-level clouds throughout the night; precipitation is unlikely.

Summary of Key Meteorological Variables
Summit temperatures will be near 6.5 C this afternoon, 2 C this evening and 1.5 C tomorrow morning. Winds will be from the east at 10-20 mph for today, switching to a more NE direction and strengthening to 20-35 mph as the night progresses. Seeing will be near 0.8-0.9 arcseconds, while precipitable water is expected to exceed 4 mm through the night.

Discussion
The tradewind inversion is expected to weaken/lift toward 12-13 thousand feet as patches of moisture begin to fill in from the east, which could contribute to periods of fog and high humidity at the summit for tonight. The inversion is set to fall apart as widespread moisture and instability drifts in, resulting in extensive fog and rain at the summit and deep convection in the area between late tomorrow morning and early Thursday afternoon, at least. While there is a possibility that the inversion will recover, the mid-level air mass will remain quite saturated for Thursday night. In addition, more widespread moisture/instability may fill into the area and erode the inversion for the following 2 nights. This could allow fog/high humidity and rain/convection to remain an issue well into the weekend. Extensive daytime clouds are possible throughout the forecast period.

There is a chance for patches of summit-level clouds filling into the area, particularly for early this evening and again toward the end of the night. Thicker more widespread clouds are expected to drift in from the east, likely blanketing summit skies for at least tomorrow night. Lots of residual broken mid-level clouds will likely remain in the area (particularly to the south and SW) for Thursday and Friday night, and there is a possibility that another round of thick clouds will fill in from the east for Saturday night.

Precipitable water is expected to exceed 4 mm throughout the forecast period.

An influx of abundant moisture, instability and/or turbulence at various levels in the atmosphere will contribute to poor/bad seeing for the next 5 nights.

Outer rainbands from incoming Hurricane Madeline is expected to erode the inversion this afternoon and may contribute to periods of fog and high humidity at the summit for early this evening. There is a possibility that the inversion will briefly recover a touch between the passage of this rainband and the main body of widespread/deep moisture/instability associated with Madeline for the middle of the night. However, the latter will start to build into the area early tomorrow morning, and conditions will only grow worse thereafter. Madeline is scheduled to slowly weaken, but will maintain its Hurricane status until it passes well westward around Friday morning; this is fairly certain. How bad conditions will get at sea-level will depend on the track of Madeline, which is still a bit uncertain. The latest GFS run is starting to edge closer to what the CPHC has been suggesting and that the center of Madeline will scrape the southern tip of the Big Island around Wednesday night. This makes sense given the structual (weakening) change and its resulting steering mechanism the storm will undertake over the next 48 hours. It would not surprise me if Madeline maintains a even more westerly trajectory, given the shape of the mid/low-level ridge, its associated steering flow; this could be potentially awful for most of the Big Island between early tomorrow afternoon and late Thursday morning. Regardless of the storm's track, due to the widespread moisture surrounding the storm, I expect inoperable conditions (extensive fog/rain, convection and moderate/strong winds) to plague the summit for at least tomorrow night, and cloudy wet air mass could persist for Thursday night. There is a slight chance that some stability will be injected into the area, in the wake of Madeline, but Hurricane Lester is slated to move in from the east, bringing fresh instability/moisture to the area for the early half of the weekend. Again, expected sea level conditions will depend on the track of Lester, which is highly uncertain. Current GFS model run projects Lester to pass ~200 KM to the north and nearly parallel to the state, but the margin of error here is very large. Neverless, expect very poor/wet conditions and cloudy skies at the summit throughout most of the forecast period. For more information on Madeline and Lester, please check with the CPHC and NHC, respectively.