Rainy season off to bad start

Hopes pinned on February

29 January 2019 | Weather

Rainfall between October and December last year was less than normal but weather experts are hopeful of better rain prospects in February.

A seasonal rainfall outlook issued this week by the Meteorological Service of Namibia states that the delayed development of El Nino, coupled with other rainfall influencing developments including a weak El Nino, “opens a window of opportunity for improved rainfall performance during the period January to February 2019 than previously anticipated.”

This follows a suppressed start to the season.

Between October and December most reporting stations throughout Namibia reported “suppressed rainfall activities”, the Meteorological Service found, except for pockets of areas within the triangle of Khorixas, Otjiwarongo and Otjimbingwe and areas surrounding Steinhausen in the Omaheke Region where above-normal rainfall was experienced.

The report highlighted however that Khorixas and surrounding areas only received rain during October within one day. No rainfall was recorded in November or December.

“The suppressed rainfall over most parts of the country implies that the rainy season ended with rainfall deficit for the first portion of the rainy season (October to December 2018),” a second report on Namibia's rainfall performance in December stated.

The outlook for January to March says it is likely that Namibia will receive normal to below-normal rainfall.

For the overlapping February to April rainfall period, Namibia is likely to continue receiving “normal to below-normal rainfall except over the southern regions where below-normal to normal rainfall is anticipated.

More specifically, the report notes that for the period February to April, the north-eastern, central and north-western parts of the country pose a 40% probability of normal rainfall in those months, a 35% probability in the below-normal category and a 25% probability in the above-normal category.

Below-normal is defined in meteorological terms as within the driest third of rainfall amounts of the 30-year periods 1971 to 2000 and 1981 to 2010.

The above-normal rainfall category is defined as lying within the wettest third of recorded rainfall amounts in those 30-year spans and normal is the middle third, centred on the climatological median.

In the south, the weather experts have assigned a 40% probability in the category below-normal for the period February to April rainfall season, a 35% probability in the normal category and a 25% probability in the above-normal category.



Rainfall patterns

Rainfall performance statistics released by the Meteorological Service show that in December, rainy weather was mainly concentrated over the north-eastern sector of the country, with Rundu reporting the highest and heaviest rains within 24 hours, and a total of 136.5 mm of rainfall in December, 84% more than the normal average rainfall for that month for Rundu.

Other stations that reported high and heavy rainfall were at Ombona in the Erongo Region and at Ncamagoro in the Kavango East Region, both with 40mm of rainfall on one day.

Several December rainfall measurements showed significantly less than the normal average of rainfall received. Keetmanshoop reported no rainfall in December, compared to a relative average of 10 mm in December, and Khorixas, with zero rainfall measured in December, compared to the average normal of 15 mm.

Grootfontein, which on average receives 65.4mm of rainfall in December, reported 19.1mm, 71% below average. Okaukuejo's rainfall for December measured 7.2 mm, down by 83% from the average normal of 42.5mm in December.

Windhoek's average December rainfall was higher than usual, with 67.1 mm recorded compared to the 30.7 mm average rainfall for that month.

JANA-MARI SMITH