Thundershowers expected during the week, especially over the eastern parts where a possibility exists for storms to become severe. Dry and sunny conditions will return over the whole country by the weekend.
Summary
Very little rain occurred during the last few days over the country. A low-pressure system in the upper air that was responsible for widespread thundershowers mostly to the northwest of the country, until early last week, also moved out of the region and weakened.
Cool conditions initially in the east made way for increasing temperatures through most of the last few days. However, the hottest conditions were experienced over the southern to western parts for the country. The hot conditions over the country, associated also with a berg-wind situation over the southwestern parts, resulted from mostly anti-cyclonic circulation that dominated through the period and which reached a peak by the weekend. Such circulation patterns generally favour sunny and hot weather during summer.
The situation will be somewhat more favourable for precipitation over the country during the next few days, as an upper-air trough will deepen over the central to southern parts, resulting in thundershowers over the eastern parts while cold conditions will develop in the south. In fact, cool to cold air will invade most of the western, southern and central interior on the 30th and 31st, where temperatures should decrease by about 10°C, with minimum temperatures expected to be in the single digits over most of these areas.
The air mass from the southwest will push thundershower activity northeastwards during the week and will also enhance the severity of certain storms due to interaction with moisture further east later this week. In contrast to last week, temperatures are on average expected to be near normal over the interior, but below normal over the southern parts of the country.
Rainfall will be confined mostly to the eastern summer rainfall region, with the most favoured areas being the Highveld region and into KZN. There may well be a tendency for thundershowers to become severe over the eastern interior, especially later during the week when upper-air instability and interaction between contrasting air masses at the surface will enhance severe weather potential. The rainfall event over the eastern parts will also be associated with the influx of cooler air over most of the country later, invading the northeastern parts from the east. This will be the result of a high-pressure system ridging around the country as is very much the case during most widespread rainfall events in summer.
Current projections favour dry conditions to return by the weekend as the upper-air system moves out east, while cooler conditions may still be present over much of the interior. From Sunday (4th), given a projected increase in surface moisture, thundershowers may redevelop over the interior.
The following is a summary of weather conditions during the next few days:
Although the period will start out with isolated thundershowers over the central to western interior, falls are expected to be light in these areas, and total rainfall during this period will be below normal over most of the central to western parts of the country.
Showers are possible initially over the winter rainfall region and along the Garden Route, but these are expected to clear later on Tuesday (30th).
It will be hot, dry and windy over the northern to northeastern parts of the country on Tuesday (30th). It will become cooler from the 31st.
Temperatures over the southern, western and central parts will fall significantly (more than 10°C) early in the week. Minimum temperatures over the central parts will be single digits, with the possibility of frost in spots over the southern high-lying areas.
Temperatures will on average be near normal to above normal in the north, but below normal over the southern high-lying interior.
Scattered thundershowers will occur over the central to eastern parts from Wednesday (31st), concentrating over the eastern parts - especially the Eastern Highveld - until Friday.
Thundershowers over the eastern parts may become severe by Tuesday (mostly over parts of KZN), concentrating on the Highveld from Wednesday (30th) to Friday (2nd), with the possibility of hail.
Rainfall totals for the period will generally not exceed 50 mm except for isolated areas in KZN and Mpumalanga.
Strong southeasterlies are possible over the southwestern parts of the winter rainfall region by Wednesday (31st) and Thursday (1st).
Dry and sunny conditions will return to the entire country by the weekend when the western to central parts will become warm to hot again.
Thundershowers may redevelop over the interior from Sunday (4th) into early next week.
Seasonal overview
El Niño and seasonal forecasts
ENSO While ENSO-neutral conditions prevailed in September, signs of El Niño increased in early October 2018 as east-central tropical Pacific SSTs warmed to weak El Niño levels. Also, low level winds showed westerly anomalies in most of the last three weeks. The subsurface water temperature continued to be above-average, and increased further recently.
The official CPC/IRI outlook calls for a 70-75% chance of El Niño development during October/November, continuing through Northern Hemisphere winter 2018-19. An El Niño watch is in effect. New forecasts of statistical and dynamical models collectively favour imminent El Niño development, most likely weak to moderate strength - International Research Institute for Climate and Society http://iri.columbia.edu/
According to the International Research Institute for Climate and Society, there is a high likelihood for an El Niño during summer 2018/19. CP NASA
