Dr. Jeff Masters' WunderBlog

The weather in the region ravaged by Cyclone Nargis in Myanmar has taken a turn for the better today, after a low pressure system that brought heavy rains and 20-30 mph winds yesterday weakened and moved off to the north. This system appeared to be a threat to develop into a tropical depression yesterday, but interaction with land is hindering its development, and the low is no longer expected to become a tropical depression. You can view the latest satellite images of the low (dubbed 96B) at the Navy/NRL web site.

The monsoon is coming
However, the respite from bad weather will be short-lived, as the mighty summer monsoon is almost upon the disaster area. The Southwest Monsoon (called that because the winds typically blow from the southwest) is an annual rainy period lasting from late May to mid-September in the regions surrounding the North Indian Ocean. The monsoon forms in response to the unequal summertime heating of the air over the land and oceans. The land heats up quicker than the oceans, creating low pressure and rising air over the Indian subcontinent. Moist air from the oceans is drawn in over the land areas to replace this hot, rising air, and the moist oceanic air brings heavy rains to the region. Truly prodigious rains accompany the arrival of the monsoon. The capital of Yangon averages about one inch of rain per month in the period just before the monsoon starts, and twenty inches per month thereafter.


Figure 1. Current position of the Southwest Monsoon, (northernmost green line), compared to average. The northern edge of the monsoon is almost upon the region hit by Cyclone Nargis. Image credit: India Meteorological Department.

As of today, the edge of the monsoon was just 100 miles south of Yangon and the Irrawaddy delta region (Figure 1). The monsoon is expected to push northwards into the region by Saturday--about one week earlier than average. The monsoon will greatly complicate relief efforts in Myanmar, which can expect flooding rains and problems with mud-choked and washed out roads. The monsoon will continue to affect the area until September. One bright side: once the monsoon arrives, it greatly reduces tropical cyclone formation in the North Indian Ocean. Major tropical cyclones in the North Indian Ocean are most common in May and November, just before and just after monsoon season.

Was the population warned?
Many of you have expressed amazement that so many could die from a tropical cyclone in this day and age of satellites and modern communications. Why did it happen? I believe there are two main reasons: the historical lack of tropical cyclones that have hit the Irrawaddy delta, and the unwillingness of Myanmar's leaders to provide adequate warnings for fear of jeopardizing their May 10 referendum to consolidate their power.

I've been sent an image of the warning for Cyclone Nargis as it appeared on May 2 in one of Myanmar's main newspapers, "The New Light of Myanmar". The warnings for Nargis on the day it made landfall as a major cyclone did not make the front page, but instead were buried on page 15 of the obituaries and miscellaneous section. The story did not talk about the storm surge or the cyclone's maximum sustained winds, and only mentioned that Myanmar might experience 50 mph winds in squalls. At the time the newspaper was likely preparing this article, both the Joint Typhoon Warning Center and the India Meteorology Department were calling for Nargis to be a Category 1 or Category 2 storm at landfall in Myanmar.

Jeff Masters

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