Maunakea Weather Center

Maunakea Observatories Forecast
5 PM HST Friday 24 May (0300 UTC Saturday 25 May) 2024
Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while banding high clouds build in from the west, contributing to extensive cloud cover or even overcast skies for much of tonight.

Summary of Key Meteorological Variables
Summit temperatures will be near 2 C this evening and 1.5 C tomorrow morning. Winds will be light and from the NNW for the first half of the night, switching to a more WNW direction for the second half. Seeing will be near 0.5 arcseconds, while precipitable water is expected to exceed 4 mm throughout the night.

Discussion
A distinct inversion will continue to cap low-level moisture primarily near 7 thousand feet, and combined with the lack of organized deep moisture will ensure the summit steers free of fog and precipitation through the next 5 nights. However, there is a chance that humidity will increase toward 60-70% as patches of mid-level moisture passes through the area, mainly for Sunday and again on Tuesday night. Some afternoon clouds are possible throughout the forecast period.

High clouds will continue to fill in from the west and thicken as a narrow band of cirrus build in from the WSW, contributing to extensive cloud cover or even brief periods of overcast skies for tonight. While there is a good chance that the banding high clouds will head off toward the south and SE on Saturday, patches of mid-level clouds may continue to linger in the area while more high clouds pass to the south well into next week. There is also a possibility that a patch of thicker mid/upper-level clouds will build in from the west and pass over the summit area through much of Tuesday.

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

Relatively calm/stable skies with light/laminar NW flow at and above the summit will likely allow seeing to settle in near 0.5 arcseconds over the next 2 nights and perhaps into Sunday evening. There is a possibility for an increase in summit-level winds, which could stir up light boundary layer turbulence and contribute to a degadation and/or variability in seeing mainly between late Sunday evening and midnight Monday. Winds are set to subside and could allow for an improvement in seeing during the latter night, but there is a slight chance for an increase in thermodynamic mid/upper-level turbulence for Tuesday night.

Little change since the morning forecast...The mid/upper-level to the NW will continue to very slowly dissipate, become more shallow and shift off toward the NE through the weekend. Residual mid-level moisture surrounding the low will persist near the Big Island, contributing to high PW will into next week. Fortunately, the mid/surface ridge to the NE will continue to promote strong/steady subsidence in the area, which will help maintain the inversion near 7 thousand feet and ensure the summit steers free of fog/precipitation through the next 5 nights. The position of the low will keep the rebuilding tropical upper-tropospheric trough (TUTT) displaced further off toward the NW and probably contribute to a weaker, but broader, sub-tropical jet (STJ) to the south of the Big Island. The TUTT will have little impact on the stability of the atmosphere near the summit and the jet will allow mostly laminar westerly flow to prevail in the free atmosphere throughout the forecast period. This should allow for better than average seeing as a slightly drier mid-level air mass and light winds prevail at the summit over the next 2 nights. However, the STJ is expected to send a narrow band of cirrus over the summit, contributing to extensive cloud cover or even overcast skies for tonight. This band is set to move off toward the south by sunrise tomorrow, though there is a chance that high clouds will still be visible along the southern skies and patches of mid-level clouds may occasionally develop in the area into next week. Latest model runs suggest that the STJ will deepen a bit, resulting in an increase in summit-level winds mainly between late Sunday evening and midnight Monday. This could contribute to an increase summit-level winds, which may stir up light boundary layer turbulence and perhaps degrade seeing a bit during that period. While winds are set to subside as the jet becomes more shallow again on Tuesday, a patch of mid/upper-level clouds ushered in initially by the deepening STJ could contribute to another round of extensive cloud cover and may limit much of an improvement in seeing for that night.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Fri May 24 - 8 PM70-907-100 / 02NNW/0-100.4-0.64-6
Sat May 25 - 2 AM60-807-90 / 01.5WNW/0-100.4-0.64-6
2 PM40-605-60 / 07WNW/5-15NaN4-8
8 PM20-405-60 / 02WNW/5-150.4-0.64-6
Sun May 26 - 2 AM10-305-60 / 01.5W/5-150.4-0.64-6
2 PM0-206-70 / 06.5W/10-20NaN4-8
8 PM10-306-70 / 01W/10-200.45-0.654-6
Mon May 27 - 2 AM20-407-80 / 01WSW/10-200.5-0.84-6
2 PM40-608-100 / 07W/10-20NaN4-8
Tue May 28 - 2 AM60-806-100 / 02WNW/15-300.475-0.7254-6
2 PM60-806-100 / 07NW/10-20NaN6-10
Wed May 29 - 2 AM60-806-90 / 01.5WNW/10-200.425-0.6756-10
2 PM70-905-90 / 06.5WNW/5-15NaN8-12
Rise and Set times for the Sun and Moon
Night (HST) Sun Set Twilight End Twilight Beg Sun Rise Moon Rise Moon Set Illumination (%) RA DEC
Sat May 25 - Sun May 26 19:05 20:17 4:21 5:33 21:19 N/A 91 18 49.3 -28 43
Sun May 26 - Mon May 27 19:05 20:17 4:21 5:33 22:15 N/A 83 19 50.3 -26 48
Mon May 27 - Tue May 28 19:05 20:18 4:20 5:33 23:06 N/A 74 20 49.1 -23 19
Tue May 28 - Wed May 29 19:06 20:19 4:20 5:33 23:52 N/A 64 21 44.9 -18 31
Wed May 29 - Thu May 30 19:06 20:19 4:20 5:33 0:33 N/A 53 22 38.0 -12 45
Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Monday 27 May 2024.
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