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Western Caribbean disturbance soaking the Yucatan; record October heat in the U.S.

By: Dr. Jeff Masters, 1:28 PM GMT on October 09, 2007

A large low pressure system (94L) over the Western Caribbean continues to be a threat to develop into a tropical depression. This morning's QuikSCAT pass showed a well-defined surface circulation, with top winds of 30 mph. Satellite loops show this surface circulation is centered less than 100 miles off the Mexican coast near Chetumal. Concentrated thunderstorm activity is mostly absent near the center of circulation, but Cancun radar shows heavy rain showers in bands removed from the center moving ashore over the Yucatan. Wind shear remains below 10 knots, but given the very large amount of atmosphere 94L is trying to spin up, it may not have time to form into a tropical depression before the center moves ashore. The center should move ashore in the Yucatan between Chetumal and Cozumel later tonight or Wednesday. All hurricane hunter flights into 94L have been canceled.

Steering currents are weak in the Western Caribbean, but a slow motion to the west or northwest is expected for the next 1-3 days, which will keep the storm over the Yucatan. Heavy rains may cause flooding problems in Belize, Mexico's Yucatan, and northeast Guatemala over the next five days. Some models, such as the GFDL, predict that 94L will perform a counter-clockwise loop over the Yucatan and re-emerge into the Western Caribbean 3-4 days from now. Another round of drenching rains might then ensue over Belize, Guatemala, and Mexico's Yucatan as the storm re-intensifies. It is also possible 94L could emerge into the Gulf of Mexico or Pacific Ocean, and re-intensify in those locations.

There is a strong trough of low pressure forecast to swing across the U.S. this week, which could turn 94L northwards into Western Cuba, the Florida Keys, or Southwest Florida. The HWRF is the only of our reliable computer models forecasting such a turn, and I don't expect it to happen.

Record heat, record cold
Unprecedented heat cooked the eastern half of the U.S. during the first week of October--but record cold temperatures affected some regions of the West, as well. On Sunday October 7, and Monday October 8, hundreds of daily high temperature records were set, and many stations recorded their hottest October temperature ever (or their highest temperature so late in the year). Among these hottest ever October records:

Bluefield, VA 88
Beckley, WV 86
Memphis, TN 95
New York City, NY (Kennedy Airport) 90
South Bend, IN 89
Fort Wayne, IN 89
Indianapolis, IN 91
Jackson, KY 88
London, KY 92
Detroit, MI 90
Alpena, MI 90
Saginaw, MI 90

The heat brought an early end to the Chicago Marathon on Sunday, which was halted after the 88-degree heat sent 49 runners to the hospital. Emergency vehicles made 300 calls along the race course.

Figure 1. Departure of maximum temperature from average for Monday, October 7. Image credit: National Climatic Data Center.

Temperatures have averaged over 30 degrees above normal in some regions of the country the past week (Figure 1). On the other side of the country, though, record daily low temperatures have been recorded at a few locations in Arizona and Utah this week. The jet stream is to blame for the record heat and record cold--a sharp kink in the jet has put a persistent trough of low pressure over the Western U.S. and a ridge of high pressure over the Eastern U.S. Beginning today, this kink is expected to straighten out some, resulting in far fewer temperature extremes across the country.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.