Maunakea Weather Center

Maunakea Observatories Forecast
10 AM HST (2000 UTC) Friday 26 May 2023
Chance for fog, ice and high humidity
Moderate winds

Cloud Cover and Fog/Precipitation Forecast
There is a moderate risk for periods of fog, ice and high humidity throughout the night; precipitation is unlikely. There is a slight chance for light cirrus passing primarily along the northern skies through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 1 C this afternoon and -4 C for the night. Winds will be from the NW at 15-30 mph, with seeing near 0.7-0.8 arcseconds. Precipitable water is expected to linger in the 2.5-3.5 mm range for the night.

The inversion will remain rather elevated/indistinct as instability persists in the area probably throughout the forecast period, and there is a possibility for an influx of deeper moisture over the Big Island late in the weekend and for the early part of next week. As a result, there is a moderate/high risk for periods of fog, ice and high humidity at the summit over much of the next 5 nights. There is also a possibility for light short-lived flurries/rain mainly after Saturday night. Extensive daytime clouds are possible throughout the forecast period, and there is an outside chance for isolated afternoon convection along the Big Island slopes, mainly late in the weekend and early part of next week.

There is a possibility for light cirrus passing along the NE skies through the night. A thin band of cirrus is expected to spread in from the west and slip over or just along the southern half of the Big Island for tomorrow night. More organized, thicker clouds will quickly follow suit and/or build in from the south on Sunday, likely contributing to extensive cloud cover or even overcast skies for that night and early part of next week.

Precipitable water is expected to slip toward 2-3 mm for tonight, then increase back to 4+ mm for the remainder of the forecast period.

A mixture of instability, an elevated inversion, boundary layer turbulence and/or moderate/strong free atmospheric turbuence will contribute to mostly poor seeing over much of the forecast period There is a possibility for bad seeing should the atmosphere become fairly saturated for Sunday, Monday and Tuesday night.

Although the surface ridge will continue to sit near its climitlogical position in the NE Pacific, a very well-defined tropical upper-tropospheric trough will stretch out from the west coast to the NW of the state and out toward Guam probably well into next week. Large-scale subsidence associated with the former will be largely negated by widespread instability tied to the TUTT and especially an embedded upper-level low to to the NNE of the state. While this will likely contribute to rather indistinct/elevated inversion, the bulk of the deep moisture will rotate around the low and shift off to the east of the Big Island over the next 2 nights. Nevertheless, there is still a risk for periods of fog, ice and high humidity and a tight wind gradient along the southern flank of the low may keep winds near 20-25 mph during that time. A passing short-wave trough is expected to re-energize and contribute to a westward shift of the low late in the weekend and early part of next week. This may actually help to squeeze the tighter mid-level wind gradient westward and allow summit-level winds to taper late in the weekend. However, deepening/strengthening of the low may also drag more widespread/organized moisture in from the tropics, which could contribute to saturating much of the air mass for Sunday night and early part of next week. This will not only further increase the risk for extensive fog/ice, but also light flurries/rain at the summit during that time.
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 26 - 2 PM60-804-575 / 251NW/15-30NaN4-8
8 PM0-20Clear50 / 10-4NW/15-300.6-0.92.5-3.5
Sat May 27 - 2 AM0-20Clear35 / 5-4NW/15-300.6-0.92.5-3.5
2 PM60-804-565 / 202.5WNW/10-20NaN4-8
8 PM0-209-1060 / 15-1.5W/15-300.6-0.94-6
Sun May 28 - 2 AM20-409-1065 / 15-3W/15-300.6-14-6
2 PM70-904-1075 / 251W/10-20NaN6-10
8 PM60-808-1075 / 25-3WSW/10-200.7-1.14-8
Mon May 29 - 2 AM80-1006-1080 / 30-3W/5-150.7-1.34-8
2 PM80-1004-1090 / 600W/5-15NaN6-10
Tue May 30 - 2 AM80-1004-1085 / 50-3W/5-150.7-1.34-8
2 PM80-1004-1090 / 602WSW/5-15NaN6-10
Wed May 31 - 2 AM70-904-1080 / 50-1W/5-150.6-1.24-8
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
Sat May 27 - Sun May 28 19:05 20:18 4:21 5:33 N/A 1:36 57 11 09.0 9 04
Sun May 28 - Mon May 29 19:06 20:18 4:20 5:33 N/A 2:08 66 11 52.7 3 31
Mon May 29 - Tue May 30 19:06 20:19 4:20 5:33 N/A 2:40 75 12 36.9 -2 20
Tue May 30 - Wed May 31 19:06 20:19 4:20 5:33 N/A 3:14 84 13 22.6 -8 16
Wed May 31 - Thu Jun 01 19:07 20:20 4:20 5:33 N/A 3:51 91 14 11.1 -14 04
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Friday 26 May (0300 UTC Saturday 27 May) 2023.
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