Seasonal Rainfall Forecast March to May 2007

  1. EXECUTIVE SUMMARY

 1.1       Introduction

The Meteorological Department provides regular weather and climate early warning advisories and forecasts on 10 – day, monthly and seasonal time scales. Following the conclusion of the Eastern Africa regional Climate Outlook Forum held in Nairobi, Kenya (5-7th March 2007) and in addition to the analysis carried out by the Department, the detailed March to May 2007 seasonal rainfall forecast has been arrived at.

  • Highlights of the September to December 2006 rainy season

The September to December 2006 rainfall season was influenced by moderate El Niño conditions which matured towards the start of the season. As predicted the rains were rather poor over many parts of the country during the month of September but picked up mid October and reached peak levels in November/early December. Floods were reported in a number of places during the peak rains especially over eastern, Lake Victoria Basin and central regions and to a certain extent the western region.

  • Highlights for the January to February dry season rainfall and Forecast for March to May seasonal rainfall.

Most parts of the Eastern region and to a certain extent the Lake Basin and Central areas experienced a moderate dry season during January and February as wide areas of these regions experienced periods of rather heavy un seasonal rains.  On the other hand most parts of the north-western, northern and western regions experienced rather pronounced dry conditions as the rains were to a great extent below average for most parts of these months.

As for the forecast period of the March – May season, among the principal factors taken into account are the observed and predicted Sea Surface Temperatures (SSTs) over the tropical Pacific Ocean and over the tropical Atlantic and Indian Oceans. The patterns of anomalously warm SSTs associated with El Niño in the tropical Pacific Ocean are currently near average (neutral) but are expected to cool further during the forecast period.  Much of the Indian and southern Atlantic Ocean are warm.

For the forecast period of March to May 2007 probabilities of normal to above normal rainfall favour most parts of Lake Victoria basin, central, western, north western and central northern Uganda. On the other hand, there is an increased likelihood of normal to below normal rainfall over most parts of eastern, north eastern and south western Uganda.

The overall implication for the season is a strong likelihood of average rains over most parts of the country. Currently sporadic outbreaks of showers and thunderstorms accompanied by strong wind gusts, violent at some locations because of the present excessive heat are being experienced in several parts of eastern, central, western and south western as well as the Victoria basin. These are precursors to the start of the steady rains. 

  1. DETAILED REGION BY REGION FORECAST

EASTERN REGION

2.1.1 Eastern Lake Victoria and South Eastern (Jinja, Kamuli, Iganga, Mayuge, Bugiri, Busia and Tororo).

The region is currently experiencing occasional out breaks of showers and thunderstorms. Onset of steady rains is expected around mid – March.  The rains are expected to intensify with the main peak around early April through mid May. The decline of the rains is expected around late May and cessation is expected around early June.  Overall there is a high chance for this region receiving normal to below normal rains.

2.1.2 Eastern Central:  (Pallisa, Mbale, Sironko, Kapchorwa, Kumi, Kaberamaido, Soroti). 

This region has been experiencing a rather prolonged dry spell which is now easing up with occasional showers and thunderstorms. The occasional showers are now intensifying marking the onset of steady rains. The steady rains are expected to continue with the peak occurring around mid-April through to mid May.  The steady rains are expected to relax late May with cessation occurring around early to mid June. Overall normal to below normal rains are expected.

2.1.3 Eastern North:  (Katakwi, Moroto, Kotido, Nakapiripiriti). 

The region has been experiencing its normal prolonged dry season. The on-set of steady rains punctuated with occasional outbreaks of dry spells is expected late March / early April, the rains are expected to persist until the end of the forecast period with a peak occurring around mid-April.  Near normal to below normal rainfall is expected in this region. 

2.2 CENTRAL NORTHERN REGION

2.2.1 Eastern Parts: (Lira, Pader, Kitgum). 

The region has been mainly dry with occasional outbreaks of rain showers.  The occasional showers are expected to intensify leading to the onset of steady rains late March / early April. The peaks of steady rains are expected around late April/early May with a moderate relaxation during June.  Overall near normal to above rainfall is expected during this season.

2.2.2 Western Parts :(Gulu, Apac) 

Currently the area is mainly dry with occasional outbreaks of light rain showers.  The outbreaks of rain showers are expected to increase leading to the onset of steady around late March / early April.  The steady rains are expected to increase with peaks being experienced around mid – April and mid – May.  This will be followed by a moderate relaxation during the month of June.  Normal to above normal rainfall is expected to prevail during this season.

2.3 WESTERN REGION

2.3.1 North Western: (Moyo, Yumbe, Adjumani, Arua ,Maracha, Terego and Nebbi) 

This region is currently experiencing outbreaks of showers and thunderstorms thus ending the dry spell experienced in January and February. Steady rains are expected early April with a relaxation around late May to mid June when the main season for this region starts.  There is a high chance of this region receiving normal to above normal rainfall during March – May.

2.3.2 Western Central: (Masindi, Hoima, Kibaale, Kyenjojo, Kamwenge, Kabarole and Bundibugyo) 

The region is currently experiencing outbreaks of showers and thunderstorms but steady rains are expected around late March. Peak rains are expected around early April to mid May.  Rainfall is expected to relax late May with the cessation occurring early June.  This region is expected to receive normal to above normal rainfall.

2.3.3 South Western: (Kasese, Bushenyi, Rukungiri, Kanungu, Ibanda, Mbarara, Kiruhura, Ntungamo, Kisoro, Kabale)

Currently this region is experiencing sporadic outbreaks of showers and thunderstorms punctuated by rather long dry spells. The onset of steady rains for most of this region is expected around mid March. The steady rains are expected to increase with the main peak around mid April, the cessation is expected mid May.  Normal to below normal rainfall is expected in this region. 

2.4 LAKE VICTORIA BASIN AND CENTRAL AREAS

2.4.1 Central and Western Lake Victoria Basin: (Kalangala, Kampala, Wakiso, Entebbe, South Mpigi, Eastern Masaka, Mityana)

This region is currently experiencing out breaks of showers and thunderstorms but steady rains are expected around late March. The rains are expected to intensify with the main peak occurring around mid April and a secondary peak around mid May. The cassation is expected mid June. Overall, there are high chances of normal to above normal rainfall.

2.4.2 Western Parts of Central: (Nakasongola, Luwero, Kiboga, Mubende, Sembabule, Western Masaka, Rakai)

The region is experiencing outbreaks of showers and thunderstorms which are expected to continue leading to the on set of steady rains late March. These rains are expected to intensify with the peak occurring around mid – April and cessation late May / early June.  It is expected that most parts of this region will experience normal to above normal rainfall.

2.4.3 Eastern parts of Central: (Mukono, Kayunga)

This region is currently receiving outbreaks of showers and thunderstorms signifying the onset of steady rains.  The steady rains are expected to intensify with the peak occurring around mid – April.  Thereafter, the rains are expected to relax with cessation occurring mid- June. Overall, normal to above normal rainfall is expected.

Note:  This forecast will be updated monthly and as when necessary and the Department will keep users informed of any new developments.

EXPLANATORY NOTES TO TERMINOLOGY

Above Normal:  This is when the total rainfall is above 125% of the long term average. Impact on socio – economic activities is mostly boosted especially in the modest degrees of above average.

Normal:            This is when the total rainfall is in the range of 75% to 125% of the long term average rainfall. This range of rainfall is expected to adequately support the normal socio – economic activities for the various areas.

Below Normal: This is when the total rainfall is below 75% of the long-term average rainfall. Under this range there are high chances for socio –

economic activities being stressed; the level of stress increasing with increasing rainfall deficiency.

Accuracy:       This forecast is up to 70% accurate.  It is supported by products from Regional and Global forecast centres. It will be updated in our                          regular Bulletins and as when necessary.

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