Tornadoes, violent thunderstorms rip the U.S.; Richard dies in the Gulf of Mexico

Tornadoes, violent thunderstorms, and torrential rains are sweeping through the nation's midsection today, thanks to an explosively deepening low pressure system over Minnesota. The spectacular storm is expected to bottom out at a central pressure of 960 mb later today, the type of central pressure one commonly encounters in Category 2 hurricanes. A powerful cold front trails southwards from the storm, and this cold front has spawned an impressive squall line studded with violent thunderstorms. As many as eleven simultaneous tornado warnings have been issued late this morning for these thunderstorms, from southern Michigan to northern Mississippi. So far, the tornadoes have been embedded within the squall line, and these type of tornadoes are typically weaker EF-0 to EF-1 twisters. However, as the day progresses and the sun's heating adds energy to the atmosphere, strong EF-2 or EF-3 tornadoes are likely, if discrete supercell thunderstorms separate from the squall line and begin to evolve. So far, six reports of tornadoes touching down have been received, but only minor damage has been reported. NOAA's Storm Prediction Center has placed much of southern Michigan, eastern Indiana, and western Ohio in their "High Risk" area for severe weather. "High Risk" days occur less than five times per year, on average, and are unusual in the fall. Fall storms this intense only occur perhaps once every 5 - 10 years. You can follow today's severe weather outbreak using our Severe Weather Page and Tornado page.


Figure 1. This morning's severe weather outlook from NOAA's Storm Prediction Center puts most of Indiana and Western Ohio into their highest category for severe weather.

Richard dies
Tropical Depression Richard emerged into the Gulf of Mexico this morning after crossing the Yucatan Peninsula. However, passage over the Yucatan so weakened the storm that it has officially been declared dead by NHC. There was too much dry air and wind shear in the Gulf of Mexico to allow Richard to regenerate. Richard hit central Belize Sunday night as a Category 1 hurricane with 90 mph winds. The storm is being blamed for $18 million in damage, but no deaths were reported. Belize lost about 1/3 of its orange crop to Richard's high winds. Electrical power is still out to 30% of the country, but is expected to be fully restored by tonight.


Figure 2. Visible MODIS satellite image of Hurricane Richard taken at 4:35pm EDT 10/25/10 by NASA's Aqua satellite. At the time, Richard was a tropical depression with 35 mph winds. Image credit: NASA.

Invest 90L
A low pressure system (Invest 90L) in the middle Atlantic Ocean has developed a broad circulation, with a band of heavy thunderstorms in an arc to the north and east of the storm. This hybrid subtropical system is under a moderate 10 - 20 knots of wind shear. Water temperatures are marginal for development, just 26.5 - 27°C (26.5°C is usually the limiting SST that a tropical storm can develop at.) NHC is giving 90L a 30% of developing into a subtropical depression or storm by Thursday.

Next update
I'll have an update on Wednesday morning. I'm at the National Hurricane Center in Miami this week, as part of their visiting scientist program, and will be shadowing NHC forecasters on the evening shift Tuesday - Friday to learn more about their operations. I'll probably talk tomorrow about the severe weather outbreak, but later this week I'll talk about what a shift at the Hurricane Center is like. I also have meetings planned with scientists at NOAA's Hurricane Research Division later this week, and plan to write about some of the research missions performed during this year's hurricane season.

Jeff Masters