SYNOPTIC DISCUSSION

SATURDAY 28th  MARCH 2026 PM SHIFT

TONIGHT & TOMORROW:

The SPCZ chain remains over the islands with Vaiaata recording the peak value of 15.6mm of rain within 10 minutes in the afternoon. The TPW animation hinted high values of moisture concentrated to the northwest of the big island where most of the active convections were developing as visualized over the satellite animation in the evening.  Streamline charts drawn by both Honolulu and New Zealand Met Services showcase the aforementioned synoptic setup mapping well with the satellite loop observed across the available channels. Periods of heavy falls eased a few hours after sunset with mostly high clouds increasing cloud cover aloft as favorable area of instability resided east over American Samoa’s AOR. Although, there is a decrease in rain intensity and coverage, there is still a high chance for deep convections to occur early tomorrow as CIMMS observations agree with the vorticity signature, wind shear and availability of moisture through the vertical layers of the atmosphere. Thus, the warnings for Flood and Heavy Rain remain in force for all vulnerable locations of Samoa.

MONDAY THROUGH FRIDAY:

Unstable weather conditions will remain over the area of forecast as the SPCZ axis fluctuates along our island chain for the start of the new week. A weak low-level circulation is still predicted to the west of the Savaii early Tuesday which will exceed the steering level. This surface to mid-level development and synoptic setting is expected to drive a moderate to fresh Northerly flow over the group through mid-week, hence, maintaining moisture over the area. Intensified wind speeds are forecasted at the gradient level with short duration as it rapidly exits the region due to the extension of a ridge from the north through the latter days of this outlook period. Trade wind regime will be introduced on Thursday as the SPCZ axis migrates further southwest allowing the aforementioned ridge to take control of stable weather later in the week.

MARINE OUTLOOK:

Generally, the observed marine data show that wave and swell heights (waves: surface water movement; swells: longer-period waves from farther away) across Samoa’s waters are still below the 2.5 metre threshold, so there is no threat. Wave models suggest this will continue for the forecast period.

ADVISORIES/WARNINGS:

VALID: HEAVY RAIN WARNING

VALID: FLOOD WARNING

Weather Duty Team:

Gafa, Tuatipi, Tutasi & Uili.