Weather to improve in the next few days: Meteorology Office
The Samoa Meteorology Office has stated that we will be seeing improved weather in the next few days with wind speeds and rainfall to ease by Sunday.
According to a "Summary of meteorological parameters from the Extreme Floods" posted by the Samoa Meteorology Division on Saturday, the Divisions Prinipal Scientific Officer, Silipa Mulitalo stated that just below two months into the tropical cyclone season and we are experiencing the impact of La Nina in the South Pacific with the widespread impact of significant flooding.
“Such impacts are typical of tropical cyclone landfall, however this was caused by persistent rainfall for a long duration. River and flooding is perhaps the most common in Samoa and for yesterday’s event, the two main contributors were intense rainfall and the lands capacity to absorb water.
The catchment's capacity to soak up any further moisture exceeded considerably all throughout the country and he explained that the soils were highly saturated which caused the water flows to rise higher than its banks with higher flow velocities and as a result flow out into adjacent low lying areas.
"This is particularly a serious concern for Apia Urban Area where the drainage system may not cope,” he said.
“And because the heavy rainfall happened around high tide, the effect of raising tides further intensified the flooding exceptionally."
According to satellite imagery, it shows the synoptic weather systems in the South Pacific and that severe T.C Yasa which made landfall over Fiji is located to the southwest with convections extending as far north as Samoa.
"Major cloud developments, thunderstorms and heavy rainfall are a identified within the vicinity of our islands with rainfall estimates indicating about 20mm of rain in an hour,” Mr. Mulitalo said.
“Wind observations show 30 to 40kmph northeast and northwest winds forming a convergence pattern over Samoa, which manifested into thunderstorms and intense precipitation which led to flooding,” he said.
He stated that for the early morning, exceptional rainfall amounts have been recorded from all stations particularly from 3am to 10am, with the highest 5 minute rainfall of 11mm from Tiavi.
The chart shown in the summary shows the rainfall observation from the week, and he edxplained that It has been raining since the beginning of the week and raining heavily.
He explained that The warning threshold for rainfall was surpassed since Sunday for the whole week, so there has been so much water received on the ground and unable to runoff to the oceans especially during high tide.
“If we look at the seven day total, it gives us an idea of how to rank this week’s severe weather event to historical data. The average rainfall for Apia in December is 348mm for the whole month and almost all stations recorded well in excess in just one week. Afiamalu has a monthly rainfall average of 555mm so in comparison Afiamalu station recorded a remarkable 932mm in seven days,” he said.
According to him, it has been raining for quite some time now, and if we go back to last month’s total rainfall, the blue bars on the chart is observed rainfall in November for a number of stations and orange is the 30 year average at those locations for November as well.
"A few of these stations have recorded more this year compared to average, this means that our areas is presently favorable for cloud formation and rainfall development,” he said.
“The winds throughout this week were within the advisory and warning range. Strongest winds occurred from Monday to Wednesday with the highest gusts of 65kmph at Nafanua, higher gusts were assumed to have occurred at areas we do not have observations,” he said.
“The current situation in the South Pacific. Severe Tropical cyclone Yasa category 3 continues to move away from Fiji area and a deep cloud band extends towards Samoa with thunderstorms approaching from the west.
He stated that a weaker cloud band past Upolu to the east at 8pm tonight with minimal rainfall, however another cloud band will bring widespread rain this morning, with the potential for heavy falls.
Mr. Mulitalo further stated that it will arrive around subsiding tides thus the inundation risk is not as extreme as yesterday, however, flood warning is maintained nationwide.
“The swells approaching from the southwest are 4 to 5m which will be essential for mariners, shipping, and communities residing near the southwest of larger islands," he said.
"The current track of severe tropical cyclone Yasa maintains its south movement and will have no threat to Samoa however for the next 12 hours warnings for heavy rains flood and marine will be maintained, including advisories for wind, high surf, and coastal flood.
“We will be seeing improved weather conditions in the next few days. Wind speed and rainfall will ease by Sunday and it’s looking fine for the beginning of the new week."