SYNOPTIC DISCUSSION
THURSDAY 01st JANUARY 2026 AM SHIFT
TODAY:
Conditionally stable environment remains over Samoa’s AOR as a southerly flow dominated the surface to low-level through the early hours of today. A favorable large CAPE persist with dry slots concentrated along the mid-level atmosphere with light and variable winds strengthening to 30 knots with increasing altitude. Excellent upper divergence and outflow is focused over the northern part of the AOR and it is where the deep convective activities are located based on the satellite loop of today. Water vapor channel and TPW animation showcase our area covered by a dry airmass circulated by a moist atmospheric layer linked to TD04F situated southeast of our island chain. Meanwhile, another low-level circulation is gradually developing North of Fiji group where some active isolated cb cells are indicating growth. Latest ASCAT swaths revealed a light northwesterly wind flow prevails, thus, increasing chance of showers for windward northern locations with the possibility of a few thunderstorms over highlands assisted by sea breeze and surface heating during the morning through late afternoon.
According to the Fiji Met Service Update, Tropical Disturbance TD04F center [1003hpa] was analyzed near 18.1S 164.5W at 312100UTC. Position Fair based on Himawari-9 Vis/IR Imagery. TD04F is slow moving. Deep Convection Continues to Persist to The East of Supposed LLCC. TD04F lies in a Moderate to High sheared environment with good Upper Divergence to the East & Warm SST around 28 Degrees Celsius. Good Equatorward Outflow as well as Stronger Upper Divergence just to the East of Supposed LLCC. However, Dry Air Intrusion from The Southwest of the System as well as High Shear to the South of the System and Hinder Development. Global Models have weakened the System as it tracks Southwards.
The Potential for this System to Develop into a Tropical Cyclone remains Low in the next 24-48hrs. TD04F has a LOW chance of impacting Samoa within the next 24-28 hours.
FRIDAY THROUGH WEDNESDAY:
The abovementioned low-pressure system analyzed north of Fiji group is predicted by models to remain almost stationary whilst dragging the SPCZ western flank near Samoa. This will likely drive equatorial moisture over the island chain through the weekend maintaining a northeast flow anticipated for Sunday into the new week. Model ensembles and meteograms suggest the spread of data of the box and whisker plot indicative of large uncertainty in the prediction. However, maximum values possible for heavy falls in some areas are mainly hinted for Saturday into Sunday. The upper system will likely be a diffluence and weak divergence forecasted to drift from the southwest possibly enhancing parcel entrainment through the ceiling level. A decreasing trend in daily rainfall is predicted for the latter days of this outlook period.
MARINE OUTLOOK:
The latest marine observational data consistently shows that wave and swell heights are remaining under 2.5 meters. The wave models continue to indicate that these wave activities are expected to stay below this threshold until Friday, when a fetch area of moderate-to-fresh westerly winds is predicted to generate higher waves, with a low-to-moderate likelihood of reaching 2.5 meters from Saturday to Sunday on the western side of Savai’i island.
ADVISORIES/WARNINGS:
NONE
Weather Duty Team:
S. Gafa, A. Niko, A. Uili & S. Maualaivao.