SYNOPTIC DISCUSSION
SATURDAY 29th NOVEMBER 2025 AM SHIFT

REST OF TODAY:

The variations in erratic conditions continue to persist across the forecast area from early morning, with convective cloud bands forming in the vicinity, particularly active offshore as indicated by satellite images from this morning. These conditions maintain the vulnerability of most areas within the group, as unstable weather remains prevalent across the Area of Responsibility (AOR), attributed to the low-pressure trough that still lies over the region. The ascent sounding from Pago Pago revealed sufficient atmospheric moisture, with a Precipitable Water (PWAT) measurement of 64.16 mm, alongside an increase in instability that correlates with the broad moisture illustrated by the MIMIC Total Precipitable Water (TPW) animation loop, which coincides with a few thundery activities observed offshore as seen through satellite channels. A slight broad area of vorticity at the 850 mb level is also associated with the persistent trough and the active vertical developments due to the weakening wind shear environment and the gradual increase in upper divergence, according to CIMMS. Furthermore, the latest ASCAT swaths have shown evidence of a convergence zone approaching from the north, which is likely to contribute to the severe conditions expected to persist into the evening and through tonight. Therefore, the highlighted warning and advisory remain in effect for all land areas of Samoa, with a high probability of continued validation.

SUNDAY THROUGH FRIDAY:

Significant precipitation and instability associated with the SPCZ is expected to persist in the forecast zone on Sunday evening, with coverage and intensity increasing through Tuesday. An intriguing upper trough is projected to travel along the Jetstream flow, directing an active downstream with northwest winds of 50 knots aloft at the beginning of the new week. However, the likely prevailing flow at the steering level will predominantly be westerlies, which will become variable in the latter days. Additionally, a weak low-level circulation is suggested to be located southwest of our islands during this period, which will sustain a northwesterly flow across the region over the next four days. Consequently, isolated showers are anticipated to become more frequent on Sunday evening, increasing to scattered showers by Monday as the upper trough approaches the area of interest. Regarding mid-week conditions, a slight decrease in 12-hourly to daily precipitation is expected across the country as the surface and upper troughs shift eastward, leading to mostly fine and easing conditions likely by Thursday, continuing through the end of the outlook period, as southeasterly trades are forecasted to dominate the area of concern.

MARINE OUTLOOK:
Observations in our marine waters suggest that wave and swell heights remain under 2 meters, as reported by the Aunu’u and King-Poloa wave buoys. However, Wave Watch 3 and various global wave models are forecasting the onset of a northerly swell surge with periods exceeding 20 seconds, expected from late Monday through Tuesday of the upcoming week. Additionally, another northerly surge with periods slightly greater than 12 seconds is predicted to reach our northern marine waters late tomorrow. Consequently, the issuance of a marine advisory is probable for tomorrow as we continue to monitor these peak wave periods anticipated for our local seas.

ADVISORIES/WARNINGS:
VALID: HEAVY RAIN WARNING

VALID: FLOOD ADVISORY

Weather Duty Team:
Gospel Niko, Lao Ioane Tuatipi, Ne’emia T & Siala Maualaivao