Maunakea Weather Center

Maunakea Observatories Forecast
6 AM HST (1600 UTC) Tuesday 23 April 2024

Cloud Cover and Fog/Precipitation Forecast
The summit will remain clear, dry and stable 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 NNE at 5-15 mph for today, switching to a more easterly direction and increasing to 10-20 mph for the night. Seeing will be near 0.55-0.6 arcseconds, while precipitable water is expected to be in the 0.6-0.8 mm range for the night.

A well-defined tradewind inversion will continue to cap low-level moisture at or below 9 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.

Skies will remain predominately clear through at least Thursday night. Scattered high clouds are set to spread in from the west and pass over the summit area for Friday night.

Precipitable water is expected to dip to 0.6-0.8 mm for tonight, only to settle back in around 1.25-1.5 mm for the next 4 nights.

While mostly calm/stable skies with light/laminar northerly flow will prevail in free atmosphere, mid-level flow is expected to pick up and will likely degrade seeing toward more average-like values over the course of the night. There is a chance for light boundary layer turbulence, which may lead to average/poor seeing for Wednesday night, but seeing should improve toward 0.4-0.5 arcseconds as winds subside through Thursday night. An increase in free atmospheric turbulence result in minor degradation in seeing over the following 2 nights.

The mid/surface ridge will continue to sit to the north of the state and promote steady/strong subsidence in the area through the week. This subsidence will easily offset the tropical upper-tropospheric trough (TUTT) stretching out from the west coast, to the west of the Islands and out toward Guam during that time. It will also maintain a well-defined inversion at or below 9 thousand feet and ensure a dry/stable summit-level air mass throughout the forecast period. The TUTT's associated sub-tropical jet (STJ) will persist to the south of the Big Island, which will allow for clear/calm skies to prevail in the free atmosphere through at least Thursday night. Unfortunately, the mid-level portion of the ridge is expected to expand and strengthen over th enext 48 hours, before retracting and lifting further off toward the NE on Thursday. This could contribute to an increase in mid-level flow and minor boundary layer/low-level turbulence, probably resulting in some degradation/variation in seeing during that period. Seeing is expected to improve again with the contraction of the ridge late Thursday night and into Friday night. There is a possibility that the sub-tropical jet will lift northward and bring scattered high clouds as well as light free atmospheric turbulence to the area over the weekend.
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celsius) (Dir/MPH) (Arcseconds) (mm)
Tue Apr 23 - 2 PM0-20Clear0 / 07NNE/5-15NaN0.8-1.2
8 PM0-5Clear0 / 02.5ENE/10-200.45-0.650.6-0.8
Wed Apr 24 - 2 AM0-5Clear0 / 02E/10-200.475-0.7250.6-0.8
2 PM0-20Clear0 / 07E/10-20NaN0.8-1.2
8 PM0-5Clear0 / 02ENE/10-200.55-0.851-1.5
Thu Apr 25 - 2 AM0-5Clear0 / 01.5E/10-200.475-0.7251-1.5
2 PM0-20Clear0 / 06.5ESE/5-15NaN1-2
8 PM0-5Clear0 / 01.5ENE/5-150.4-0.61.25-1.75
Fri Apr 26 - 2 AM0-10Clear0 / 01E/5-150.35-0.551.25-1.75
2 PM20-409.5-100 / 06SE/5-15NaN1-2
Sat Apr 27 - 2 AM20-409-100 / 00.5SE/5-150.425-0.6751-1.5
2 PM40-608.5-100 / 05.5SSE/5-15NaN1-2
Sun Apr 28 - 2 AM20-409-100 / 00SW/5-150.425-0.6751.25-1.75
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 Apr 23 - Wed Apr 24 18:52 19:59 4:40 5:48 18:40 6:30 100 14 26.1 -17 13
Wed Apr 24 - Thu Apr 25 18:52 20:00 4:39 5:47 19:34 N/A 98 15 15.6 -21 49
Thu Apr 25 - Fri Apr 26 18:53 20:00 4:39 5:46 20:30 N/A 94 16 08.7 -25 31
Fri Apr 26 - Sat Apr 27 18:53 20:01 4:38 5:46 21:28 N/A 88 17 05.2 -27 59
Sat Apr 27 - Sun Apr 28 18:53 20:01 4:37 5:45 22:27 N/A 80 18 04.5 -29 00
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Tuesday 23 April (0300 UTC Wednesday 24 April) 2024.
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