Maunakea Weather Center

Maunakea Observatories Forecast
630 AM HST (1630 UTC) Monday 07 July 2025
Warning(s)
Moderate/strong winds

Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while light cirrus gradually dissipates overhead through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 7 C this afternoon, 2 C this evening and 1.5 C tomorrow morning. Winds will be from the east at 25-40 mph for today and 30-45 mph for the night. Seeing will exceed 1 arcsecond, while precipitable water is expected to linger near 0.8-0.9 mm for the night.

Discussion
A distinct tradewind inversion will continue to cap low-level moisture primarily near 7 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived throughout the forecast period.

Light cirrus will continue to build in from the south over the next 6-12 hours and gradually dissipate over the summit area through Tuesday night. Mostly clear skies will prevail for the following 3 nights.

Precipitable water is set to linger near 0.8-0.9 mm through Tuesday night, then settle in around 0.7 mm for the following 3 nights.

Deep easterly winds are expected to stir up boundary layer turbulence and contribute to poor/bad seeing through Wednesday night. While deep easterly winds will persist below 25 thousand feet into the weekend, winds near summit-level are set to taper significantly and light westerly flow will prevail in the free atmosphere. This, combined with a dry/stable air mass, should allow for excellent seeing on Thursday and Friday night.

The mid/surface ridge will continue to sit to the north of the state probably well into next week, while an upper-level ridge will prevail overhead and to the east, before dissipating in response to an upper-level low developing to the north around mid-week. Nonetheless, steady/strong subsidence will persist near the state, which will easily maintain a well-defined tradewind inversion near 7 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. PW will also benefit from the subsidence and presense of the upper-level ridge, likely settling in near 0.7-0.8 mm (or less) during that time. Unfortunately, the upper-level ridge will also help augment deep easterly flow below 20 thousand feet, which will stir up boundary layer turbulence and contribute to poor/bad seeing over the next 3 nights. Winds in the lower half of the atmosphere are set to subside with the dissipation of the upper-level ridge by Thursday morning, which should allow seeing to settle back in around 0.4 arcseconds for the following 2 nights.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Mon Jul 07 - 2 PM40-609.25-100 / 07E/25-40NaN0.8-1.2
8 PM20-409.5-100 / 02E/30-451-20.7-0.9
Tue Jul 08 - 2 AM10-309.5-100 / 01.5E/30-451-20.8-1
2 PM0-209.25-100 / 07E/25-40NaN0.8-1.2
8 PM0-209.5-100 / 02E/20-350.8-1.60.7-0.9
Wed Jul 09 - 2 AM0-209.5-100 / 02E/20-350.8-1.60.7-0.9
2 PM0-20Clear0 / 08E/15-30NaN0.8-1.2
8 PM0-10Clear0 / 03.5E/15-300.7-1.10.6-0.8
Thu Jul 10 - 2 AM0-10Clear0 / 03E/10-200.55-0.850.6-0.8
2 PM0-20Clear0 / 010E/5-15NaN0.8-1.2
Fri Jul 11 - 2 AM0-10Clear0 / 04.5NE/0-100.3-0.50.6-0.8
2 PM0-20Clear0 / 09.5SSE/5-15NaN0.8-1.2
Sat Jul 12 - 2 AM0-10Clear0 / 03.5ESE/0-100.3-0.50.6-0.8
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
Mon Jul 07 - Tue Jul 08 19:15 20:28 4:26 5:39 N/A 3:56 94 17 04.9 -28 35
Tue Jul 08 - Wed Jul 09 19:15 20:28 4:27 5:40 17:35 4:50 98 18 01.8 -29 05
Wed Jul 09 - Thu Jul 10 19:15 20:28 4:27 5:40 18:29 5:47 100 18 59.5 -28 06
Thu Jul 10 - Fri Jul 11 19:15 20:28 4:27 5:40 19:19 N/A 99 19 56.5 -25 37
Fri Jul 11 - Sat Jul 12 19:14 20:27 4:28 5:41 20:06 N/A 97 20 51.6 -21 47
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Monday 07 July (0300 UTC Tuesday 8 July) 2025.
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