September 10 is the statistical high point of the Atlantic Basin hurricane season. This year has been unusually quiet, but there are signs that the atmosphere is becoming more agreeable to tropical development.
In the Pacific, Hurricane Norbert scraped Baja California and spun some moisture northward into the southwest, enhancing the seasonal monsoon.
Phoenix experienced heavy rains and even parched southern California got some.
An early-season cold blast in the plains and midwest will bring shivers to midwesterners who are imagining another winter like the last one; but there are signs the pattern is changing in the US.
Not so in Europe, where a broad ridge in the jet stream is refusing to budge. Temperatures across the continent are unseasonably mild, with records in some areas.
Monsoon flooding in India and Pakistan claimed several hundred lives last week. Unfortunately this is almost an annual occurrence, as much of the population of the Indian subcontinent lives in flood-prone places.
Let’s go around the world.
Where Are The Atlantic Hurricanes?
As the calendar slips past the halfway point of the Atlantic Basin hurricane season (Sept. 10), there have only been four named storms — just one-third the average total for the season. The summer weather pattern has been characterized by dry African air over virtually the entire central and eastern Atlantic. Tropical activity has been limited to three hurricanes near the Atlantic coast, and recently tropical storm Dolly in the Gulf of Mexico.
Now things appear to be changing. Easterly waves coming off Africa are encountering a moister environment; with winds favorable at all levels of the atmosphere, things could spin up in the next few weeks. By the end of September, the ‘Cape Verde’ season for hurricanes in the eastern Atlantic comes to an end, as upper level winds become unfavorable for tropical development. After that, action shifts to the Caribbean, Gulf of Mexico, and western Atlantic. There is a secondary maximum of activity in October, as storms form on frontal systems which reach the Gulf of Mexico and southern Atlantic coast.
In the Pacific, Hurricane Norbert passed just offshore of Baja California, close enough to cause minor damage. The moisture from Norbert combined with moisture from Dolly in the Gulf of Mexico to bring flooding rains to Phoenix and much of the desert and adjacent mountains — technically this is part of the late summer monsoon. These are not the deluges that we will discuss in connection with the Indian monsoon, but drainage in the southwest is often difficult, and rains that would be no problem elsewhere can cause floods in Arizona.
Before we finish the subject of Atlantic hurricanes, yesterday was the anniversary of the most deadly storm in US hurricane history — the 1900 Galveston hurricane which killed more than 8000 people.
The forecast of the day showed a low pressure system in the Gulf and nothing more than a few showers was predicted. Today there would have been several days of advance warning and large-scale evacuations.
On the other hand, though loss of life would probably be in single digits, loss of property — simply because there is more, and more valuable, property — would be very high.
Cold Air Plunges Into American Heartland; Shades Of Last Winter?
An initial surge of cool air ended the heat wave in the center and east of the United States except for the far south. Another shot of even colder air is heading southward this week and will reach the Gulf Coast.
The jet stream is looking ominously like last winter, but if the longer term forecasts can be believed, there will be a moderation in the short-term, and there is an indication that more moderate temperatures might prevail over the eastern United States later in the fall.
The indication is that a powerful branch of the polar vortex is beginning to dominate the eastern Pacific Ocean, This will force a ridge, or at least a zonal (westerly) flow across much of the US. Let’s hope so.
The Indian Monsoon
Monsoon rains in India and Pakistan killed hundreds last week.
Just four years ago, thousands lost their lives in the same areas.
Though increasing rainfall worldwide can be expected to cause flooding locally in the future, overpopulation and shoddy housing construction are certainly factors in the loss of life and property in Asia.
So What’s With All The Rain?
The atmosphere is warming. Warmer air (even a degree warmer) can hold substantially more moisture than air at the slightly lower temperature. Furthermore, the atmosphere is showing a tendency to more persistent patterns. That means it rains longer and harder in a particular area.
So far, the result of climate change is localized extreme weather. No one knows whether the trend will accelerate or modify, but it would be a good idea if the upcoming international conference on climate change in Bonn, sponsored by the United Nations, had a serious discussion.
How’s the weather changing where you are?
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