During May 2002, two tropical storms formed south and north of the equator. The below animated IR satellite shows clouds and storms from May 1st to May 14th, 2002. You can identify two storms forming, and then moving away from the equator. Those two storms were supported by a shared factor: A Westerly Wind Burst (WWB).
Animated Movie of Arabian Sea Tropical Storm in May 2002. Please wait for the movie to load. Image retrieved from NOAA National Climatic Data Center
Westerly Wind Burst
Westerly wind burst refers to westerly winds forming over or near the equator. Before the formation of the two tropical storms, a westerly wind burst formed over the equatorial western Indian Ocean, between the Arabian Sea and the southwest Indian Ocean. The below image shows how far westerly winds deviated from a long-term average (vector winds anomaly) between April 30th and May 3rd at an altitude of 1500 meters above sea level. Winds speeds were between 9 to 12 m/s, or 32 to 43 Km/hr above average.
Anomaly 850 mb wind vector (m/s) April 30 - May 3, 2002. Notice the large area of yellow/red shading, which corresponds to above-average winds blowing from the west. Image retrieved from Earth System Research Laboratory plotting page.
Such unseasonal westerly winds caused horizontal vorticities north and south of the westerly wind burst. This, along with other favorable factors like sea surface temperatures, existing convective activity, and absence of disruptive winds over a deep layer of the atmosphere, triggered the circulation of two tropical storms. However, later as the storms formed they faced stronger wind shear, giving insight into the weakening trends of the storms and lack of organized convection in some days.
Circulation favored north and south of a westerly wind burst.
Tropical Storm ARB 01
The storm that formed between May 6th and 10th over the Arabian Sea was an early tropical storm in 2002 North Indian Ocean tropical storm season. It moved west-northwest rounding a ridge of a subtropical high located over India. It made landfall over southeast Oman as a tropical storm, and then it was downgraded to a tropical depression soon after landfall. It caused flooding in parts of Thofar region of Oman. Although it lost its tropical storm status, the storm didn’t dissipate immediately. It moved northward then northeastward, reaching parts of southern UAE and northern Oman as a remnant tropical low pressure (see animated movie). Remnants of tropical lows, after being downgraded from tropical storm status, continue delivering rainfall along their path but with diminishing risk of high winds.
Interestingly enough, the remnants of this tropical low delivered as much as 200 mm of rain to Hamim, a southern town in the UAE, according to a report from UAE National Centre of Meteorology. This was mostly likely caused by thunderstorms associated with low forming between May 11th and May 12th.
Tropical Cyclone Kesiny
The storm that formed over the southwestern Indian Ocean developed into a category 1 tropical cyclone Kesiny. It was a late-season storm that formed between May 2nd and May 11th. It impacted Madagascar as a tropical storm and caused flooding and damage to properties.
Conclusion
A westerly wind burst (WWB) forming in late April and early May 2002 over the equatorial western Indian Ocean helped trigger circulation north and south of the westerly wind burst. Aided by other favorable factors for tropical storm formation, the WWB was a key factor in the formation of an early-season Arabian Sea tropical storm and a late-season southwestern Indian Ocean tropical cyclone.