Maunakea Observatories Forecast
9 AM HST (1900 UTC) Wednesday 18 September 2024
|
Warning(s)
None
Cloud Cover and Fog/Precipitation Forecast
The summit will remain dry and stable, while high clouds build along the northern skies through the night.
Summary of Key Meteorological Variables
Summit temperatures will be near 8 C this afternoon, 3 C this evening and 2.5 C tomorrow morning. Winds will be light and from the east for today, switching to a more northerly direction through the night. Seeing will be near 0.4-0.5 arcseconds, while precipitable water is expected to be in the 1.5-2 mm range for the night.
|
 |
|
Discussion
A fairly distinct tradewind inversion will continue to cap low-level moisture primarily near 7-8 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. Daytime clouds will be minimal and short-lived into next week.
More organized widespread high clouds are set to develop to the NW of the state over the next 12 hours, and may send scattered to broken cirrus into the summit area through the next 3 nights. There is a possibility for periods of extensive cloud cover mainly for Thursday night. Most of the upper-level clouds are set to shift off toward the east of the Big Island on Saturday, but there is a chance that patches of mid-level clouds will build in from the north and linger in the area for Saturday and perhaps Sunday night.
Precipitable water is expected to drop into the 1.5-2 mm range for tonight, increase subtly to 1.75-2.25 mm for the next 2 nights, then may increase to 3-4 mm over the weekend.
Winds above 10 thousand feet will remain quite light, and combined with a generally calm/stable air mass at and above the summit, should allow for good/excellent seeing over the next 3 nights, particularly Friday night. While the air mass will remain very stable into next week, there is a possibility that westerly flow above 18 thousand feet will begin to increase, which could increase free atmospheric turbulence and result in a minor degradation in seeing for Saturday and Sunday night.
The 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. This subsidence will easily maintain a fairly well-defined tradewind inversion ar or below 9 thousand feet and ensure a dry/stable summit-level air mass through the next 5 nights. An upper-level ridge will also linger to the south of the Big Island for another 12-24 hours, then will gradually weaken and flatten out over the remainder of the week. While this ridge may still promote some degree subsidence near the summit, it will mainly help to keep the tropical upper-tropospheric troughs and embedded upper-level lows at bay further to the north. This will rule out an instability in the area and allow very calm/stable skies with light winds to prevail in the free atmosphere into the weekend. In addition, light/variable mid-level flow will prevail near the state as the mid-level portion of the ridge remains displaced further to the north and stretch across most of the Pacific into next week. These conditions should allow for good/excellent seeing at the summit over the next 3 nights. There is a possibility that as the upper-level ridge dissipates that an upper-level low to the NNE of the state will spread southward, increasing shear/turblence in the free atmosphere, which may contribute to a degradation in seeing as the weekend progresses. This low is not expected to affect the stability of the atmosphere, though it (and another low) could send mid/upper-level clouds into the area over much of the next 5 nights.
|
|
5 Day Forecast Summary (Graphical Trend)
| HST |
Cloud |
Fog/Precip |
Temp |
Wind |
Seeing |
PW |
| Cover (%) |
Height (km) |
Probability (%) |
(Celsius) |
(Dir/MPH) |
(Arcseconds) |
(mm) |
| Wed Sep 18 - 2 PM | 0-20 | 9-10 | 0 / 0 | 8 | E/0-10 | NaN | 1.5-2.5 |
| 8 PM | 20-40 | 9-10 | 0 / 0 | 3 | ENE/0-10 | 0.35-0.45 | 1.5-2 |
| Thu Sep 19 - 2 AM | 30-50 | 9-10 | 0 / 0 | 2.5 | NNE/0-10 | 0.35-0.45 | 1.5-2 |
| 2 PM | 40-60 | 8-10 | 0 / 0 | 8 | NNE/0-10 | NaN | 2-3 |
| 8 PM | 60-80 | 8-10 | 0 / 0 | 3 | NNE/0-10 | 0.4-0.5 | 1.75-2.25 |
| Fri Sep 20 - 2 AM | 60-80 | 8-10 | 0 / 0 | 3 | N/0-10 | 0.4-0.5 | 1.75-2.25 |
| 2 PM | 40-60 | 8-10 | 0 / 0 | 9.5 | NNE/5-15 | NaN | 2-3 |
| 8 PM | 20-40 | 8-10 | 0 / 0 | 5 | ENE/5-15 | 0.3-0.4 | 1.75-2.25 |
| Sat Sep 21 - 2 AM | 20-40 | 8-10 | 0 / 0 | 4.5 | ENE/0-10 | 0.3-0.4 | 1.75-2.25 |
| 2 PM | 20-40 | 7-8 | 0 / 0 | 8 | SE/5-15 | NaN | 2-3 |
| Sun Sep 22 - 2 AM | 20-40 | 6-8 | 0 / 0 | 2 | SSE/0-10 | 0.4-0.6 | 2-4 |
| 2 PM | 20-40 | 6-8 | 0 / 0 | 7 | S/5-15 | NaN | 3-5 |
| Mon Sep 23 - 2 AM | 0-20 | 6-7 | 0 / 0 | 2 | SSW/0-10 | 0.45-0.65 | 3-5 |
|
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 |
| Wed Sep 18 - Thu Sep 19 |
18:30 |
19:34 |
4:57 |
6:01 |
18:56 |
N/A |
97 |
0 57.4 |
6 39 |
| Thu Sep 19 - Fri Sep 20 |
18:29 |
19:33 |
4:57 |
6:02 |
19:38 |
N/A |
92 |
1 53.0 |
13 33 |
| Fri Sep 20 - Sat Sep 21 |
18:28 |
19:32 |
4:57 |
6:02 |
20:21 |
N/A |
84 |
2 50.4 |
19 30 |
| Sat Sep 21 - Sun Sep 22 |
18:27 |
19:31 |
4:58 |
6:02 |
21:09 |
N/A |
74 |
3 49.9 |
24 07 |
| Sun Sep 22 - Mon Sep 23 |
18:26 |
19:30 |
4:58 |
6:02 |
22:01 |
N/A |
64 |
4 50.9 |
27 06 |
|
Forecast Issued by: Ryan Lyman
Next update at 5 PM HST Wednesday 18 September (0300 UTC Thursday 19 September) 2024.
|
Additional Information
For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.
NWS Hawaiian Islands Synoptic Discussion and Guidance
Honolulu National Weather Service Data and Products
|
