The degree and severity of the weather along the ITCZ varies, based on the degree of convergence. The zone of disturbed weather may be as little as 20 to 30 miles in width or as much as 300 miles. Under typical conditions, frequent rainstorms, cumulus and cumulonimbus-type clouds, and local thunderstorms occur. Violent turbulence may be associated with these storms, and cloud bases may lower to below 1,000 feet, or even be indistinguishable, in heavy showers. Their tops frequently exceed 40,000 feet. An extensive layer of altocumulus and altostratus usually occurs, due to the spreading out of the upper parts of the convective clouds. These layers vary in height and thickness with the currents of the air masses. At higher levels, a broad deck of cirrostratus spreads out on both sides of the zone. Icing in the heavy cloud masses is likely to reach serious proportions at altitudes above 15,000 feet, as this is roughly the average freezing level in equatorial regions.

Surface winds are generally squally in the areas of heavy showers. Usually, the winds in the squalls do not exceed 15 to 25 knots, but winds of 40 to 50 knots or higher have been reported. Visibility is usually good except when reduced by the heavy shower activity.

The intensity of the ITCZ varies inter-diurnally, from day to day, and to a lesser degree annually. Over ocean areas, precipitation reaches its maximum just before dawn, with a minimum occurring in the late morning or early afternoon. With the exception of coastal areas under the influence of onshore winds, the reverse is true over landthe daily maximum occurs in the late morning.

Through the use of satellite data, the seasonal meridional displacement of the ITCZ band has been determined. See figure 9-3-6. Imagery has