Also, anomalously wet NAMs in Arizona are strongly anti-correlated with anomalously dry summers in the mid-west. Although regional climate models have succeeded in reproducing some features of the NAM, its onset, strength and regional extent are not well predicted, and a physical understanding of key processes governing its life-cycle remain elusive.
It is characterized by winds that blow northerly off the Pacific Ocean during warmer months and southerly from the land during cooler months of the year. Although the Gulf Coast of the United States is prone to weather patterns with monsoonal tendencies, consistent winds characteristic of true monsoons are not established there.
Not only is there a complete seasonal reversal of the wind, but the rainfall regime is typically monsoonal. The winter period, from November to January and from March to April according to latitude and other factors, is very dry.
The rainy season begins earlier May in the south and progressively later farther north, coming at the end of June in southern Mexico. It concludes at the end of September in the north and as late as early November in the south.
The result is a rainy season that increases in duration with decreasing latitude; it lasts three months in southern Mexico and from six to seven months in Costa Rica. Latitude for latitude, this is a subdued replica of the Indian monsoon. In North America the relatively low latitude and the orientation of the land-sea boundary on the Gulf of Mexico are quite favourable to monsoonal developments.
During the summerlow atmospheric pressure is frequent over the heated land. The northeasterly trade winds are consequently deflected to become easterly, southeasterly, or even southerly winds. In general, Texas and the Gulf Coast of the United States may be completely overrun by a shallow sheet of oceanic air, which may continue for a long distance inland.
The rainfall regime does not reveal any marked monsoonal pattern. There are mostly two, three, or even four minor peaks in the sequence of monthly rainfall totals.
Neither the summer onshore wind nor the winter offshore wind is persistent enough to constitute a monsoonal sequence, even though monsoonal tendencies are quite evident.The death toll could have been much worse, officials said, because the building, which houses a nursery school, collapsed half an hour before children were due to arrive at 9am.
Monsoon (/ m ɒ n ˈ s uː n /) is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea.
Usually, the term monsoon is used to refer to the rainy phase of a seasonally changing pattern, although. The North American monsoon is known to many as the Summer, Southwest, Mexican or Arizona monsoon.
  It is also sometimes called the Desert monsoon as a large part of the affected area are the Mojave and Sonoran deserts. The North American Mesoscale Forecast System (NAM) is one of the primary vehicles by which NCEP's Environmental Modeling Center provides mesoscale guidance to .
Monsoon onset and early developments.
As the high-sun season (that is, the Northern Hemisphere summer) moves northward during April, India becomes particularly prone to rapid heating because the highlands to the north protect it from any incursions of cold air.
The NAM(North American Monsoon) share the same characteristics as the Asian Monsoon. There is a shift in wind and barometric pressure, because Monsoon means seasonal shift in .