Maunakea Weather Center

Maunakea Observatories Forecast
6 AM HST (1600 UTC) Tuesday 13 May 2025
Warning(s)
None

Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while banding thin high clouds build in from the SW throughout the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 9 C this afternoon, 4 C this evening and 3.5 C tomorrow morning. Winds will be from the NW at 5-15 mph, easing and switching to a more NE direction through the night. Seeing will be near 0.45-0.5 arcseconds, while precipitable water is expected to be in the 0.7-0.9 mm range for the night.
Discussion
A distinct inversion will continue to cap low-level moisture near 8-9 thousand feet and ensure a dry/stable summit-level air mass through at least early Thursday afternoon. There is a possibility that an influx of upper-level instability and patches of moisture will erode the inversion, which could increase the risk for fog, ice and high humidity at the summit through Thursday night and especially for the following 2 nights; precipitation is unlikely. Daytime clouds will be minimal and short-lived through Wednesday, but could pick up on Thursday and turn extensive for Friday and Saturday, only to taper again for Sunday.

Banding thin cirrus is expected to build in from the south over the next 24 hours and could contribute to extensive cloud cover toward the end of tonight and especially for Wednesday night. While this band is expected wrap northward around sunrise Thursday, thicker mid/upper-level clouds may fill in from the south for that night. Patches of thicker clouds or even isolated convection could also develop in the area, particularly along the northern skies for Friday and Saturday night.

Precipitable water is expected to settle in the 0.7-0.9 mm range for tonight, trend toward 1.5 mm through Wednesday night, then could jump to 4+ mm for the following 3 nights.

While light/calm and stable conditions will prevail in the mid-level air mass, persistent upper-level dynamic turbulence will likely keep seeing near 0.45-0.5 arcseconds through Wednesday night. Upper-level flow is set to abruptly weaken early Thursday morning, but there is a possibility that a more unstable air mass and moisture will weaken the inversion, which could begin to degrade seeing through Thursday night and perhaps contribute to poor/variable seeing for Friday and Saturday night. There is also a possibility for brief increase in boundary layer turbulence, mainly around Friday morning.

The mid/surface ridge will continue to sit to the north of the state and promote steady/strong large-scale subsidence in the area through the week. Initially, this subsidence will help maintain a well-defined inversion near 8-9 thousand feet and ensure a dry/stable summit-level air mass through at least Thursday afternoon. The sub-tropical jet will also linger overhead, transporting cirrus over the summit area through the next 2 nights. At first, most of these clouds will remain quite scattered and thin, but banding cirrus is expected to quickly fill in from the SW over the next 24 hours, contributing to extensive cloud cover mainly for Wednesday night. In addition, persistent moderate/strong upper-level free atmospheric turbulence associated with the STJ will likely keep seeing near 0.45-0.5 arcseconds over the next 2 nights. The STJ is set to shift off toward the east in response to an upper-level low developing over the state on Thursday. While this help open up skies and allow light/variable winds to prevail in the free atmosphere, instability associated with the low may erode/weaken the inversion and increase the risk for fog, ice and high humidity at the summit through Thursday night. This risk will increase further as mid-level moisture/clouds build in from the south for the following 2 nights; precipitation is unlikely throughout the forecast period. The unstable air mass may also degrade seeing after Thursday night, and there is an outside chance that isolated convection will develop in the area, particularly along the northern skies and mainly between sunrise Friday and Saturday afternoon.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Tue May 13 - 2 PM10-309.5-100 / 09NW/5-15NaN0.8-1.2
8 PM20-409.5-100 / 04N/5-150.4-0.60.7-0.9
Wed May 14 - 2 AM40-609-100 / 03.5NE/0-100.35-0.550.7-0.9
2 PM80-1008-100 / 07.5ENE/0-10NaN0.8-1.2
8 PM80-1008-100 / 02.5E/0-100.35-0.551-1.25
Thu May 15 - 2 AM60-807-100 / 01.5E/0-100.4-0.61.25-1.5
2 PM40-606-920 / 05ESE/5-15NaN2-4
8 PM40-606-810 / 00.5ESE/10-200.45-0.753-5
Fri May 16 - 2 AM40-606-830 / 5-0.5SSE/15-250.5-0.94-6
2 PM70-904-990 / 503SE/10-20NaN4-8
Sat May 17 - 2 AM20-405-875 / 25-1.5SSE/10-200.5-0.94-6
2 PM60-804-990 / 402.5SSW/5-15NaN4-8
Sun May 18 - 2 AM10-306-865 / 15-2S/5-150.5-0.94-6
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
Tue May 13 - Wed May 14 18:59 20:10 4:26 5:37 19:59 N/A 97 16 44.0 -27 51
Wed May 14 - Thu May 15 19:00 20:11 4:26 5:36 20:54 N/A 93 17 39.3 -29 00
Thu May 15 - Fri May 16 19:00 20:11 4:25 5:36 21:47 N/A 87 18 35.7 -28 44
Fri May 16 - Sat May 17 19:01 20:12 4:25 5:36 22:38 N/A 80 19 31.8 -27 01
Sat May 17 - Sun May 18 19:01 20:12 4:24 5:35 23:25 N/A 71 20 26.4 -23 56
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 13 May (0300 UTC Wednesday 14 May) 2025.
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