Dan's Wild Wild Science Journal

NASA Modis image of tropical disturbance off of Florida. Pressures are dropping and upper level winds are favourable for development.

There are strong signs that the area of disturbed weather in the Gulf is beginning to get organized today. Pressures are dropping and there seems to be a circulation already present. I suspect the the folks at the NHC in Miami will begin advisories on it later today.

Tropical Cyclone heat potential is based on the depth of the warm water, not just the surface sea water temp.

If it makes it to tropical storm strength it will be named Danielle.

While it is a bit early to talk about the track, the GFDL model is indicating that a landfall somewhere around Louisiana or Mississippi is possible late Friday night. Keep in mind, that the steering currents are very weak and this could change dramatically.

HOW STRONG COULD IT GET?

Could this system reach hurricane status? Yes, but it would be tough to get that strong by landfall. The Gulf is very warm but the tropical cyclone heat potential is not overly impressive. Still it is near the Gulf loop current and that may be helpful.

A good tropical storm may actually be quite helpful to farmers in the southeast who are suffering through an intense heatwave and drought. It’s 37.5C here in Huntsville as I type this.

That’s 100°F on the old scale.

More soon…

Dan

Colder than normal water is already appearing in the Equatorial Pacific (NOAA)

One of the reasons for the forecasts of a an active hurricane season is the predictions that La Nina would develop this summer. Remember that La Nina is an ocean circulation phase that brings unusually cold water to the surface of the Tropical Pacific.

These are the temperature probabilities for a normal/above/below normal autumn (September through Novermber). Click for full resolution image.

Well, it has started and most of the ocean atmosphere models are predicting a moderate to strong event.

This has more impact than just the number of hurricanes. NOAA revised their 2010 hurricane prediction down somewhat today but they are still predicting a 70% chance of 4-6 major hurricanes (Earlier typo said 406- that would be exceptionally bad ). La Nina is a big factor in that.

The colder tropical waters cause a shift in the jet stream. This makes it possible to make a decent prediction of the fall and winter ahead. Here in the Southeastern USA we tend to have a dry fall with normal to above normal  temps. The winter tends to be drier than  normal and sometimes a bit on the mild side.

What about where you live?
The chart at the right shows the probabilities for temperatures during a La Nina event. The image is for the period from September through November.

Take a look at the Northeast USA and Eastern Canada. The chart shows that during a La Nina year the odds are VERY low that the autumn will be below normal. The odds are higher that it will be near normal and the odds are higher still that it will be a warm autumn.

This does not mean that it will not be colder than normal. It just means that in the past this happened rarely.

You can see more of these graphics for your part of the world at the IRI website here. Precipitation maps are also available.

In my last post I gave some of the reasons I thought we would see a very active hurricane season. Here is what the NOAA folks think. They released their forecast for the 2010 season today.

As I expected it looks like it will be a mean year. Possibly one of the all time most active years. Here are NOAA’s numbers:

An 85% chance of an above normal season.

A 70% probability for each of the following ranges of activity this season:

• 14-23 Named Storms,
• 8-14 Hurricanes
• 3-7 Major Hurricanes
• An ACE range of 155%-270% of the median.

From NOAA/TPC

The ACE stands for Accumulated Cyclone Energy Index (Developed by NOAA).  It’s a measure of the total amount of energy from all the storms in a particular season. (In the same basin) NOAA’s official definition: The ACE index is a wind energy index, defined as the sum of the squares of the maximum sustained surface wind speed (knots) measured every six hours for all named systems while they are at least tropical storm strength.

An average year brings about 6 hurricanes and 10 tropical storms. So this is a forecast of a possible hyperactive season.

Could we still see a normal season?

Yes!

El Nino may linger and wind shear may not be as weak in the tropical Atlantic as forecasted. The odds are heavily against those things happening though.

For more on the reasons why see my previous post.

Church in Dekalb County Alabama after the EF3 tornado Saturday. Pic taken by Katie Johnson.

The last several posts have been about the high risk of tornadoes over the Southeastern United States on Saturday.

Library in Albertville, AL. Image from Teresa Reno.

You probably have already heard of the tornado that hit Yazoo City in Mississippi . It left 10 dead and horrible damage.

Later Saturday night, the tornadoes dropped again from new thunderstorms. These were much closer to home. We were on the air many hours as the storms moved across North Alabama into NW Georgia.

There were three EF 3 tornadoes across North Alabama. Storm survey teams from the national Weather Service in Huntsville estimated the winds were at around 140 mph.

The twister that hit Albertville was at one point over  1 km wide!

Image courtesy Teresa Reno in Albertville.

The Albertville Tornado was on the ground for nearly 30 km. It caused major damage in Albertville, and in the Dekalb County town of Geraldine.

I know a lot of people have had their lives turned upside down by these storms. There were 30+ injuries, but thankfully no deaths!

I cannot begin to tell you how happy that makes those of us who forecast them. I include those of us on TV and the meteorologists who work for NOAA.

The Storm Prediction Center in Norman Oklahoma has upgraded the moderate risk of severe weather to a HIGH RISK for a large area of North and Western Alabama and much of Mississippi for Saturday.

Numerical weather models are indicating that conditions will be very favourable for tornadoes Saturday in Alabama. The "Significant Tornado Algorithm" is unusually high for a severe weather event.

New model guidance tonight indicates that wind shear and instability will be very conducive for the formation of super-cell thunderstorms and some long track tornadoes.

The greatest threat will exist from mid morning Saturday through the early evening hours over the high risk area. A large moderate risk area surrounds the high risk.

If you live in a mobile home in the high risk area, you should make plans to go to a better shelter when a tornado watch is issued. Your risk of being injured is much higher in a mobile home.

A very strong low level jet stream is already developing tonight and this will aide in supplying a deep layer of warm moist air to the region ahead of a strong cold front. The winds are increasing with height and are also veering from south to west as you get higher. This combination will allow thunderstorms to grow very strong and last for several hours.

Winds aloft measured by the Doppler Radar in Columbus Miss. Notice the winds near the ground are from the SE while at 11,000 feet they are from the west at 50 kts. Each hash on the flag is 10 kts. A triangle is 50 kts.

Any severe storms or tornadoes that develop will be moving from southwest to northeast at speeds of 80-90 km/hr (50 mph+).

Be safe,
Dan