HORSE LATITUDES – SOMETIMES A HURRICANE STALLER!

The Horse Latitudes are a belt of weak winds between latitudes 25 and 35 in the belt of subtropical high pressure.

This slowing or blocking barrier that restricts, or slows, a tropical storm’s northward advance has produced extreme floods three times this season. The first one was from BERYL, which stalled over north Florida after moving across Jacksonville during the last week of May. Four weeks later, Tropical Storm DEBBY was blocked three days over the nnortheast Gulf of Mexico south of Tallahassee. Upper level winds from the west sent multiple rounds of rain over northeast Florida causing record, or near record, flooding of inland creeks and rivers. The third blocking event took place for ISAAC on the Louisiana – Mississippi Gulf coast. LESLIE and MICHAEL are the fourth and fifth stalled storms this season, having been slowed to a crawl in the middle Atlantic Ocean east of Bermuda. Fortunately, no flooding there! This season has already produced 14 tropical storms, but five of of them have been parked or slowed to a crawl for a few days.

This subtropical high pressure belt shifts with the seasons, closer to latitude 35 in the late summer, but closer to latitude 25 in the late winter. They separate the prevailing westerlies in the temperate latitudes to the north from the easterly trade winds in the tropics.

I often marvel at nature’s mechanism for transporting the earth’s surplus of heat in the tropics through the horse latitudes to the polar regions. Scattered showers in the tropics on the large scale are similar to beads of perspiration that pop out of our skin on a hot day. Our sweat will roll down while in nature the vertical convection turns into horizontal winds that become part of the general circulation of our planet.Examples of local winds are Texas northers, Atlantic nor’easters, South America’s pamperos and Mediterranean siroccos. On the continental scale are the cold, dry winter monsoons and the warm, moist/wet summer monsoons.

Fifty years ago, there was a project that studied the effect of cloud seeding on hurricanes. It was called Stormfury.They attempted to shift the strongest convection and high winds of the hurricane’s eye wall farther away from the storm’s center to a weaker feeder band. I always liked Dr. Joanne Simpson’s description of the hurricane’s operation. She said that the fuel of tropical heat and vapor was being sucked into the feeder bands, whose vertical motions were like pistons of an engine that created the fierce winds of the hurricane engine.

The past few days, LESLIE and MICHAEL have been revving their engines, waiting to latch onto a cold front or dip in the jet stream to run their course into a whirlpool of a cold polar low pressure system. Meanwhile, we’re watching a cold front approaching our area that may consume the last remnant of ISAAC this weekend. I like this time of year because I can watch football and the weather at the same time!

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