Little change to 90L

The extratropical low pressure system (90L) approaching North Carolina has weakened some over the past 24 hours, and has a much reduced chance of developing into a subtropical storm. The National Hurricane Center (NHC) is giving 90L a less than 20% chance of developing into a depression or tropical/subtropical storm, and anticipates not writing any more special advisories on it. Last night's ASCAT pass saw a large area of 35 mph winds to the north and east of the center, and buoy 41048 to northeast of 90L's center was seeing sustained E winds of 31 mph, gusting to 36 mph this morning. Bermuda radar showing an area of moderate to heavy rain has now moved north of the island, and seas are running 10 - 15 feet in the outer waters of Bermuda today.


Figure 1. Visible satellite image of 90L and the Central American disturbance this morning.

Strong upper-levels winds out of the west are creating about 20 knots of wind shear over 90L, and the shear has been gradually decreasing over the past day. Visible satellite loops show that 90L has a well-defined surface circulation. The main thunderstorm activity is in a large curved band to the north and northeast of the center. This band is several hundred miles removed from the center, which is characteristic of subtropical storms. Sea surface temperatures are near 24°C today and will remain in the 23 - 24°C range the next two days. These relatively cool SSTs have hampered formation of much heavy thunderstorm activity, as has the presence of a large area of dry air to the west, as seen on water vapor satellite loops .

The system will move slowly towards the Southeast U.S. coast today, making its closest approach to the coast on Wednesday, when most of the models indicate the center will be 300 - 500 miles southeast of Cape Hatteras, North Carolina. All of the major models currently predict that 90L will not make landfall, but will move slowly eastward out to sea on Thursday, when a trough of low pressure moving across the Eastern U.S. picks up the storm. There presently isn't much to be concerned with about this storm, though Bermuda may get more heavy rain and high seas from the storm late this week as it moves out to sea. Wunderbloggers Weather456 and StormW have more on 90L.

Central American disturbance
An area of disturbed weather has developed just off the Pacific coast of Guatemala. The disturbance will move inland over Central America during the last half of the week, potentially bringing flooding rains to portions of Guatemala, El Salvador, Honduras, and Nicaragua. There is the potential for the disturbance to push into the Western Caribbean late this week and pose a threat to develop into a tropical depression. While there is high wind shear over the northern Caribbean, shear should be low enough to allow development should the disturbance stay in the southern reaches of the Caribbean. Any storm that develops in the Caribbean in the coming week would get steered to the northeast and will not pose a threat to the Gulf of Mexico.

Tornadoes rip through the Plains
The Storm Prediction Center logged 17 reports of tornadoes yesterday, with twisters reported in South Dakota, North Dakota, Nebraska, Oklahoma, and Texas. In addition, there were 158 hail reports and 126 reports of damaging winds. Fortunately, there were no deaths or injuries reported, and it was a good day for the Vortex2 tornado field research project. Former wunderblogger Mike Theiss caught up with a very picturesque tornado near Faith, South Dakota, and has posted some spectacular video of the tornado.


Figure 2. Large tornado near Faith, South Dakota on May 24, 2010 just misses hitting a church. Image credit: Mike Theiss, ultimatechase.com. Check out his spectacular video of the tornado.

I'll be back later today to discuss how a hurricane might affect the oil in the Gulf of Mexico.

Jeff Masters