Maunakea Observatories Forecast
5 PM HST Friday 04 September (0300 UTC Saturday 5 September) 2026
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Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
There is a small risk for periods of fog/high humidity, mainly toward the end of the night; precipitation is not expected and skies will remain predominately clear.
Summary of Key Meteorological Variables
Summit temperatures will be near 6.5 C this evening and 6 C tomorrow morning. Winds will be light and variable, with seeing near 0.4-0.5 arcseconds for the night. Precipitable water is expected to be in the 0.9-1.1 mm range throughout the night.
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Discussion
While the inversion will remain fairly well intact near 7-8 thousand feet into early Saturday afternoon, mid/low-level moisture will continue to scrape the southern tip of the Big Island and could contribute to short-lived fog/high humidity at the summit overnight. Deeper more widespread moisture will begin to fill in and erode the inversion early Saturday evening, likely allowing the air mass to become quite saturated probably through into Tuesday night. This will significantly increase the risk for fog, high humidity and light rain at the summit during this period. Daytime clouds could pick up on Saturday and turn extensive for Sunday through Tuesday, then taper again on Wednesday.
Skies will remain predominately clear for tonight. There is small chance that patches of thicker clouds will develop along the NE skies as the weekend progresses, while more widespread thick clouds build in from the south late Saturday night. This latter set will likely contribute to extensive cloud cover or even overcast skies for Sunday night, then gradually break up, opening skies over Monday and Tuesday night.
PW is expected to linger primarily near 1 mm for tonight, then jump toward 10 mm through Saturday night and probably 15+ mm for Sunday and Monday night. There is a possibility that it could begin to decrease on Tuesday.
Seeing is expected to settle back in around 0.4-0.5 arcseconds as a pocket of calm/stable air mass fills in and light easterly flow prevails at and above the summit for tonight. However, another influx of widesprad moisture and turbulence will likely degrade seeing through Saturday night and probably contribute to bad seeing for the following 2 nights. A very modest improvement in seeing is possible as the air mass begins to dry out, though there is also a chance for an increase in boundary layer turbulence again for Tuesday night.
No change since the morning forecast....A persistent surface ridge will continue to sit in the NE Pacific well into next week, while a rather tight upper-level ridge lingers just NE of the state, before dissipating in response to an upper-level low developing to the north over the weekend. Nevertheless, the surface ridge will promote steady large-scale subsidence through much of the state, while the presence of the upper-level ridge will help displace the tropical upper-tropospheric trough (TUTT) and sub-tropical jet (STJ) off toward the northwest, minimizing widespread instability/turbulence in the area into the weekend. While this will should allow for low PW and good/excellent seeing over much of tonight, bands of moisture from Hurricane Lowell to the SW may scrape the Big Island and perhaps bring short-lived fog/high humidity at the summit mainly during the second half of the night. Lowell is set to meander westward rather harmlessly to the south over the next 18-24 hours, then take on a more northerly trajectory as it's drawn toward aforementioned developing upper-level low during the second half of the weekend (likely passing near Kauai early next week). Hurricane Karina, on the other hand, approaching from the far east is set to encounter increasing shear from this developing upper-level low and fall apart to the NE over the weekend. There's lots of uncertainty, due to the number of moving parts, particularly the location/intensification of this upper-level low and the interaction with Lowell/Karina (as well as a number of detailed factors). Nevertheless, it looks like the low will also draw widespread moisture in from the tropics (along with outer rainbands from Lowell) over the Big Island area during the second half of the weekend and into the early part of next week. This could result in rather wet/cloudy conditions for the summit between late Saturday night and Tuesday evening. There is a chance that the air mass will begin to dry out as the bulk of the moisture detrains into the surrounding air mass and/or lifts northward through Tuesday night.
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5 Day Forecast Summary (Graphical Trend)
| HST |
Cloud |
Fog/Precip |
Temp |
Wind |
Seeing |
PW |
| Cover (%) |
Height (km) |
Probability (%) |
(Celsius) |
(Dir/MPH) |
(Arcseconds) |
(mm) |
| Fri Sep 04 - 8 PM | 0-10 | Clear | 5 / 0 | 6.5 | NE/0-10 | 0.4-0.5 | 0.9-1.1 |
| Sat Sep 05 - 2 AM | 0-10 | Clear | 15 / 0 | 6 | NW/0-10 | 0.375-0.525 | 0.9-1.1 |
| 2 PM | 40-60 | 4-5 | 60 / 10 | 9 | W/5-15 | NaN | 3-6 |
| 8 PM | 40-60 | 5-7 | 30 / 5 | 4 | W/5-15 | 0.5-0.8 | 4-8 |
| Sun Sep 06 - 2 AM | 60-80 | 4.5-8 | 75 / 30 | 3 | W/5-15 | 0.6-1 | 6-10 |
| 2 PM | 80-100 | 4-10 | 95 / 90 | 6 | SW/0-10 | NaN | 10-20 |
| 8 PM | 80-100 | 4-10 | 95 / 90 | 3 | S/0-10 | 1-2 | 15-20 |
| Mon Sep 07 - 2 AM | 80-100 | 4-9 | 95 / 90 | 3 | SSE/10-20 | 1-2 | 15-20 |
| 2 PM | 80-100 | 4-10 | 95 / 90 | 7 | SSW/15-30 | NaN | 15-20 |
| Tue Sep 08 - 2 AM | 60-80 | 4.5-8 | 90 / 30 | 4.5 | SSW/10-20 | 0.8-1.6 | 10-15 |
| 2 PM | 60-80 | 4-8 | 90 / 50 | 8 | N/5-15 | NaN | 10-15 |
| Wed Sep 09 - 2 AM | 20-40 | 4.5-6 | 65 / 15 | 3.5 | NNE/15-30 | 0.5-1.1 | 6-10 |
| 2 PM | 40-60 | 4-6 | 50 / 10 | 10 | NNE/15-30 | NaN | 4-8 |
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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 |
| Fri Sep 04 - Sat Sep 05 |
18:43 |
19:48 |
4:53 |
5:58 |
0:19 |
N/A |
37 |
5 51.9 |
27 39 |
| Sat Sep 05 - Sun Sep 06 |
18:42 |
19:47 |
4:53 |
5:59 |
1:24 |
N/A |
26 |
6 55.5 |
26 19 |
| Sun Sep 06 - Mon Sep 07 |
18:41 |
19:46 |
4:54 |
5:59 |
2:31 |
N/A |
17 |
7 56.8 |
23 16 |
| Mon Sep 07 - Tue Sep 08 |
18:40 |
19:46 |
4:54 |
5:59 |
3:36 |
N/A |
9 |
8 54.5 |
18 48 |
| Tue Sep 08 - Wed Sep 09 |
18:39 |
19:45 |
4:54 |
5:59 |
4:38 |
17:13 |
4 |
9 48.5 |
13 20 |
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Forecast Issued by: Ryan Lyman
Next update at 10 AM HST (2000 UTC) Tuesday 8 September 2026.
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Additional Information
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This message is also available at the MKWC road conditions page.
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