East Coast Storms

A low pressure area that developed along a weakening cold front has intensified substantially over the warm waters of the Gulf Stream. Although surface winds are strong enough to be a tropical storm, the system does not really appear to be "tropical", at least not at this point. Current satellite imagery reveals a structure more similar to a "subtropical storm". There is a tight circulation of cloud bands, but not continuous convection in all quadrants or concentrated near the center. It also has some characteristics of an early fall "nor'easter".



Tropical storms are primarily driven by latent heat release from an inner core of thunderstorms with a broad area of outflow above the low. This deep warm core of rising motion is related to the relatively small area of intense low pressure at the surface. In contrast to most extratropical (i.e. not tropical) cyclones, thermal wind arguments imply that the strongest winds in a tropical cyclone will be near the surface rather than near the tropopause. With the current system, the center does not appear to be very convectively unstable and it looks like it will take on a more extratropical character over the next couple days. In any case, it will bring some messy conditions along much of the Eastern Seaboard, but probably no reason for hysteria. There is also a good discussion on Jeff Masters' Wunder Blog.

Another area of interest, to the east of the Bahamas, is definitely tropical and may have some potential for development. But it's relatively unlikely to impact the United States.

First Day of Fall . . . or Spring?

It was a nice first day of fall across most of the United States today. But in the Southern Hemisphere it's the first day of spring. In some of the higher elevations of South Africa that meant a surprise snow storm that has caused problems for traffic in the KwaZulu-Natal and Eastern Cape areas.

Monsoon Flooding in West Texas?

The extensive rains across northern Mexico and West Texas from the retreating North American monsoon are bringing historic flooding to the Rio Conchos and Rio Grande. As reservoirs on the Rio Conchos overflow, the downstream cities of Ojinaga (in Chihuahua, Mexico) and Presidio (in Texas) have watched flood waters breach their levees. The deaths of the U.S. and Mexican directors of the International Boundary Waters Commission and Rio Grande Council of Governments in a plane crash while surveying the flood have added to the tragedy.

The Long Reach of Ike

While news coverage of the devastation from Hurricane Ike has somewhat been in competition with election and financial news, and the problems are less dramatized than with Katrina, it's important to consider how broad a swath of the country has been impacted by this storm. While Hurricane Katrina effectively wiped out infrastructure from southern Louisiana to central Mississippi, the rapid movement of Ike brought major problems all the way up to the Canadian border. This is shown dramatically by the 24 hour radar-estimated precipitation through Sunday morning.



The combination of flooding and high winds have left millions of people homeless or without power as far away as western Pennsylvania! On the other side of Ike's (fourth!) landfall, the rebuilding process is challenging the residents of Grand Turk, Inagua, Haiti, eastern Cuba, and western Cuba. The wipeout of Galveston should be compared to the destruction that Grand Turk has sustained from when the hurricane was still a Category 4 on the Saffir-Simpson scale, or the misery of Gonaives, Haiti after being inundated by four tropical cyclones in a row.

A Tropical Plume

The big news story lately has of course been Hurricane Ike. However there was also an interesting situation further to the west, before the landfall of Ike. From northern Mexico up into West Texas and Oklahoma, there was a persistent swath of cloud cover and rain. In spite of some analyses, this was not primarily due to interaction with a frontal zone. Instead, it was due to a plume of mid-level tropical moisture being blown northeastwards from Tropical Storm Lowell in the Pacific. In terms of winds or direct impacts, Lowell was never much of a storm. But its remote impacts through this plume of moisture were fairly significant. To some extent this pattern simply extended the influence of the North American Monsoon System further east into the Plains than usual. Because of the relatively wet ground in northern Mexico, it was feared that there could have been particularly bad flash flooding if Ike had tracked to the west over the region. The area of East Texas that was traversed by Ike was actually somewhat in need of rain, although they obviously could have done without the high winds.

Between Storms?

A preliminary description of impacts of Gustav on the Ark-La-Miss region is now available. Many homes in Louisiana and Mississippi remain without power. Now all eyes are on Hurricane Ike, with its 135 mph winds and a forecast that takes it over the Turks & Caicos Islands, the southern Bahamas, Cuba, and then into the Gulf of Mexico.



In central Mississippi, Saturday turned out remarkably cool and fall-like. In spite of official forecasts for a high in the low 90s that were revised to 86, the mercury actually struggled to even reach 80 under a light north breeze.

More on the Way and Some Change in the Air

As people return to south Louisiana and Mississippi, they're finding a mess and a long wait for power restoration, and have been largely forgotten by the media. Meanwhile the tropics continue to cook up more storms. Tropical Storm Hannah may have struggled and appear relatively wimpy, but it's unwelcome excursion southward brought another onslaught of misery to northern Haiti. While it was stuck in an area of with no significant upper-level steering currents, it made an unusual cyclonic loop.


Further out, we have Ike and Josephine. In all probability, Josephine will be a "fish" storm that just spins around in the open ocean, and is not expected to intensify significantly anyway. Ike is another matter. After a dramatic period of intensification yesterday, it is expected to enter the less favorable environment that Hannah has struggled in. It will probably approach the Florida as a significant hurricane, but hopefully no longer as a Category 4 storm.

Meanwhile, central Mississippi had a bit of a change today. Not only did the sun finally come out for a while, but the first weak cold front of the fall pushed through. It's always nice to have dewpoints drop from the mid-70s to the mid-60s. Of course, the reality is that it won't last very long.