The socio-economic impacts of floods calls for improved understanding of flood drivers. While the large-scale circulation anomalies associated with rainfall anomalies is a well-studied, the interaction of the phases of the Indian Ocean Dipole and the El Niño Southern Oscillation with rainfall anomalies over Tanzania is comparatively less understood. This paper fills this knowledge gap by studying the circulation anomalies associated with heavy rainfall events over northern Tanzania during the 2011 October-December season. A total number of 28 heavy rainfall events were observed, whereby 8, 11, and 9 events are recorded during October, November, and December, respectively. Bukoba is the only region that experienced more heavy rainfall events during each month of the study. Analysis of circulation anomalies reveals that heavy rainfall events are significantly related to moisture flux convergence that was transported through the northeasterly, southeasterly, and westerly pathways. The remarkable active upward motion that is conducive for heavy rainfall events also occurs over northern Tanzania. The moisture flux in October and November was under the influence of the cyclonic circulation over the south-central Indian Ocean and Indian Ocean Dipole. In December, westerly from the Congo basin forest play a significant role in enhancing the moisture flux. The results demonstrate the interplay between Indian Ocean Dipole and westerly in modulating moisture flux over northern Tanzania at a sub-seasonal time scale. The current study offers useful angles of contribution in understanding the mechanism controlling the country’s weather, therefore improving forecasting accuracy.

洪水的社会经济影响要求提高对洪水驱动因素的了解。虽然对与降雨异常相关的大规模环流异常进行了充分研究，但对印度洋偶极子和厄尔尼诺南方涛动的相位与坦桑尼亚降雨异常的相互作用的了解相对较少。本文通过研究与 2011 年 10 月至 12 月季节期间坦桑尼亚北部强降雨事件相关的环流异常，填补了这一知识空白。共观测到 28 次强降雨事件，其中 10 月、11 月和 12 月分别记录了 8、11 和 9 次。布科巴是唯一一个在研究的每个月都经历了更多强降雨事件的地区。环流异常分析表明，强降雨事件与通过东北、东南和西风通道输送的水分通量辐合显着相关。有利于强降雨事件的显着的积极向上运动也发生在坦桑尼亚北部。10月和11月的水汽通量受到印度洋中南部和印度洋偶极子气旋环流的影响。12 月，来自刚果盆地森林的西风对提高水汽通量起到了显着的作用。结果证明了印度洋偶极子和西风在亚季节时间尺度上调节坦桑尼亚北部的水分通量方面的相互作用。