FORECAST DISCUSSION

FRIDAY 15thMAY 2026 AMSHIFT

TODAY & TOMORROW:

Fair weather conditions dominate the islands as the Southeast trades remain prevalent over the forecast area. A broad dry airmass was depicted over the radiosonde data with the absence of any upper mechanism removing air from the atmospheric column for further cloud development. Although instability is present, moisture may be insufficient to trigger long-lived convective activities within the now-cast period. The feathery and wispy cirri-form clouds were dominating the SWP view from the Himawari IR loop early this morning. Such is evident of the jet stream directing drier polar airmass aloft. Majority of models are suggesting similar stable weather conditions which was experienced yesterday to persist throughout the rest of today. The eastward progression of the intensified high-pressure system currently located over the Tasman Sea is anticipated to drive slightly strengthening southeasterlies across the southern coast for tomorrow which may assist sea breeze convergence and contribute to localized convections in the late afternoon.

SUNDAY THROUGH THIURSDAY:

The abovementioned high-pressure system is predicted to redirect the SPCZ closely to the south of the island chain by Sunday. However, although the instability and moisture may be concentrated over the vicinity through Monday, the SPCZ is expected to remain weak. Fresh southeast to East winds will dominate the southern side of the islands with the upper westerlies swerving more Northwesterlies allowing moist airmass at the ceiling level. This synoptic setup will likely trigger outflow and parcel entrainment to further boost convective cycle within cb clouds. In addition, these particular days are expected to be the only days within this outlook period where the steering level starts to gain moisture according to modelled ECMWF sounding trace. A probable low-circulation is predicted to develop over Fiji group tracking southeastward causing a Northwest flow over the group in the latter days. This weak low-level circulation has a very low potential to develop into a Disturbance, Depression or TC prior to the aforementioned period.

MARINE OUTLOOK:

The latest marine observations from Aunu’u and King Poloa wave buoys as well as altimeter data indicate that wave heights continue to fluctuate near 2 metres. Furthermore, the high-pressure system located west of New Zealand, continues to slowly move eastward while generating elevated waves and swells which are predicted to affect Samoa’s southern seas tomorrow night. The timing of these wave activities could be affected by this month’s highest tide forecasted at 06:10am on Sunday. These severe weather conditions warrant the issuance of the Marine Advisory particularly for Samoa’s Southern Marine Waters.

ADVISORIES/WARNINGS:

VALID: MARINE ADVISORY – SOUTHERN MARINE WATERS

Weather Duty Team:

Gafa, Niko, Huch & Tutasi.