The Southwest Monsoon is characterized by southwesterly winds that blow across the Arabian Sea, Bay of Bengal and South China Seas in response to a temperature gradient that develops as the central portions of the Asian continent warm with the summer months.

Typically, the monsoon in the Arabian Sea begins in early June, with the peak occurring in mid July and then waning by the end of August/early September. The area of strongest winds develops in association with the Somali Low-Level Jet, which develops off the Somalia coast.

The 2008 Southwest Monsoon was characterized by an early onset _ the onset of the monsoon across the Arabian Sea occurred about a week earlier than normal. As a result, heavy conditions associated with the monsoon developed sooner than normal across the Arabian Sea. However, on the whole, the 2008 Monsoon was near-average in terms of strength over the course of the June-August time period (Figure 1).

The major feature of the Monsoon of 2008 was the extent of the conditions across the basin: the core of heaviest conditions was displaced slightly further north than average, but more notably, did not extend as far east through the basin. An easterly anomaly developed east of 65E, south of 15N, along the southwestern Indian Coast, which was present throughout the season. So although conditions were near average in strength, the duration that vessels spent in the conditions was shorter than average as they transited the Arabian Sea either eastbound or westbound (although conditions on average were heavier for vessels sailing into and out of the Persian Gulf).

To present, data from June and July 2009 (Figure 2) indicate that the monsoon of 2009 has been below average in intensity compared to climatology. However, in looking more closely at each month, one will note that the cumulative average of the two months is based on the fact that the month of June was below average in strength of conditions. July, on the other hand, was stronger than average _ with gale force conditions stretching farther north and east into the central portions of the Arabian Sea than average. As a result, vessels transiting the Arabian Sea in July 2009 were subject to stronger conditions, for longer durations, compared to both climatology and for July 2008.