SYNOPTIC DISCUSSION

THURSDAY 22nd JANUARY 2026 PM SHIFT

TONIGHT:

Moist and unstable atmospheric conditions persist over Samoa as a trough of low-pressure remains within the vicinity, bringing cloudy periods and brief heavy falls as recorded in some areas today. Meanwhile, active convections lie to the north of Samoa as a result of the South Pacific Convergence Zone (SPCZ). The afternoon ascent from NSTU Pago Pago (00z) indicates an unstable atmosphere as reflected by a CAPE of 1735 J/kg and precipitable water reaching 61.42mm. MIMIC Total Precipitable Water (TPW) imagery reveals good moisture advection over the region which continues to sustain convective developments. Strong vorticity signals persist just north of the group at 850 mb, indicating strong cyclonic curvature of the SPCZ. In addition, upper data shows strong southeasterly winds at the upper-levels with strong lower convergence and upper divergence to the north, contributing to conducive conditions that maintain active convections to the north. For tonight, expect cloudy periods with isolated showers, brief heavy falls in some areas and thunderstorms. Expect gusty winds during heavy showers.

According to Fiji RSMC analysis, Tropical Depression (TD06F) lies to the southeast of New Caledonia and moving southeast at about 20 knots. The system lies under low to moderate wind shear with deep convection displaced to the southeast. GLOBAL MODELS HAVE PICKED UP THE SYSTEM WITH LITTLE INTENSIFICATION. TD06F IS EXPECTED TO EXIT RSMC NADI'S AOR LATE TONIGHT. THE POTENTIAL FOR THIS SYSTEM TO DEVELOP INTO A TROPICAL CYCLONE IS VERY LOW.

FRIDAY THROUGH WEDNESDAY:

Global weather models suggest that the South Pacific Convergence Zone (SPCZ) will be the primary weather driver for Samoa throughout this outlook period. A surface high-pressure system, expected to centre east of Australia, will steer the ascent of the SPCZ and cause it to shift slightly north of Samoa from later tomorrow. Model consensus has consistently shown deteriorating weather conditions associated with this system, which is likely to prompt an upgrade to current advisories, likely in the next 12 – 24 hours. The SPCZ is forecast to remain nearly stationary just offshore to the north, extending its associated rain bands over the islands during this period. Areas of upper-level divergence aloft will enable and sustain unsettled conditions across the islands.

MARINE OUTLOOK:

The latest marine observations from the Aunu’u and King Poloa wave buoys, as well as altimeter data, continue to indicate that wave and swell heights remain well below 2 metres. Global wave models suggest this trend is likely to persist through at least Friday. From Saturday, increased wave activity may enter the forecast area and is likely to exceed 2.5 metres, reaching around 3 metres, due to wind-driven waves associated with the presence of the SPCZ.

ADVISORIES/WARNINGS:

VALID: HEAVY RAIN ADVISORY

VALID: FLOOD ADVISORY

Weather Duty Team:

Kalapani, Kalolo, Maualaivao & Tavana.