Paul_Dellegatto's Blog

Well, you can't blame it on global warming as May will go down as a much cooler than normal month across continental United States. You can blame it on La Nina. Yes, cooler Pacific waters have resulted in an amplified jet stream over the United States and the tornado numbers are off the scale. Unoficially, 1191 tornadoes so far and counting. Tornadoes most often form along air mass boundaries. However, the presence of a fast moving jet stream is critical to aid in the rotation of supercell thunderstorms. May is close to the peak of the severe weather season and the monthly tornado statistics should soon begin to fall as we move into the summer season.

One of the parameters we look at as we try to predict the number of tropical systems in the Atlantic is the water temperature of the equatorial Pacific. The same La Nina that is aiding in tornado development will more than likely aid in the number of tropical systems in the Atlantic. Even if La Nina moderates into a neutral state there should not be any inhibiting factor from the Pacific. It is important to remember that there are MANY factors including Atlantic water temperatures, Saharan dust, and average atmospheric pressure that contribute to tropical storm/hurricane development. Some factors that are present now may not be present in August and September and vice versa.

FINALLY! It has been a long time, but finally we saw showers pop up around the region today. For many areas, it was the first rain seen in over a month. Lawns are brown and wildfires are popping up. As dry as it has been, it is perfectly normal to go weeks with no rain in April and May. We are in between seasons. Winter cold fronts can not make it this far south so there is little chance of a cold front producing rain while there is not enough low level moisture for the summer rainy season to start. It won't be long now. The summer rainy season is right around the corner.

I am not sure if you caught this weekend headline. "Study: Climate change not behind hurricanes" Tom Knutson, a respected scientist has actually changed his position. He has warned about the harmful effects of climate change and has even complained in the past about being censored by the Bush administration on past studies on the dangers of global warming. His new outlook based on new computer modeling casts serious doubts on the relationship between global climate change and hurricane development. He argues, and I do agree, is that we are in the midst of the active part of a  multidecadal cycle. We should have seen this activitity years ago. Global warming or not. It is an interesting read.

You can read the entire story at foxnews.com at the link below.

http://www.foxnews.com/story/0,2933,356549,00.html<
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Just when it looked like April was going to be a wet month the pattern has evolved into a more typical pattern for this time of year with high pressure locked in over the southeast. The result has been lots of sunshine and low humidity. The weather has been great to be outside, but the fire danger is on the rise, especially across inland areas.

Spring is the time of year that the seabreeze has a major effect on our weather. Water temps are still cool while the blazing sun warms up the land much faster than the Gulf of Mexico. When the land is heated, it rises - to replace the rising air, the wind blows in from the Gulf cooling the coastline. Sometimes we can see as much as a ten degree temperature difference beween the beaches and inland location. Notice how the temperatures flip flop at night. Air cools more efficiently over land so late night temps are often much cooler inland than at the beaches.

Congrats and best wishes to Jule McGee. Jule is a FORTY ONE year veteran of WTVT who is retiring tomorrow. He has held many behind the scene positions at WTVT, most recently as operations manager. A true character, and a guy that really cared about the success of this television station. His salty style is going to be missed.

What a great winter!

Except for the unfortunate severe weather events in the southeast, it was a delightful winter. We had a nice blend of warm days along with recurring cold fronts that resulted in only one significant freeze. It was the coldest winter since 2001. The headline was the amount of rain we received. On average, we had over ten inches of rain that should set us up nicely heading into the rainy season in a few months. Here is the latest Keetch Byram Drought Index (KBDI)

It will be a very pleasant week with clear skies and moderating temperatures. Wednesday night will feature the International Space Station passing nearly overhead.. You don't want to miss it!  Here is the info so that you can watch from home.

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It sure has been a hectic week with severe weather coverage, a freeze, and more importantly the passing of a weather legend here in the Bay Area. Dick Fletcher was our competitor, but he was a competitor that we all respected. I have gotten to know Dick over the past 18 years thru the various weather conferences we have attended. He was a gentleman who loved to talk tennis along with the ups and downs we all go thru in the television news business. It just is not the same without him here and I was honored to say a few words about him on WTSP.

Strange winter! The presence of a strong La Nina (cold Pacific waters) almost always results in a dry winter in the southeast. We have actually done very well so far this year precipitation wise with most areas receiving at least a few inches above normal rainfall. Let's hope it continues into the rainy season.

Speaking of the climate, the global temperature data is coming in and 2007 is looking like it was a colder than normal year. We will be analyzing the data and blogging about the ramifications the data has to the global warming issue.

A big congrats to Dave and Andrea Osterberg. Andrea gave birth today to Aiden, a healthy baby boy who checked in at 7lbs, 3 oz.. I spoke briefly to Dave this evening and he was his usual animated self who can't wait to get his son on the baseball field.

The new EF Scale keeps some of the basic underlying principles of the older Fujita Scale in mind, but focuses on specific, descriptive damage caused by a tornado. First, the EF Scale takes into account the type of structure damaged, using a set of 28 damage indicators.  These damage indicators range in type from small barns, to family homes, mobile homes, and even schools, shopping malls, warehouses, and various types of trees.

Next, the EF Scale determines the Degree of

Here is what we know about the relationship between global warming and hurricanes.

It is a fact, we are in the active part of a mulitdecadal-scale fluctuation of hurricane activity. These well documented cycles run between 25-40 years and rotate between above average number of storms to a below average number of storms. What we are currently experiencing is similar to the pattern that we were in during the late 1920s to the late 1960s. When we analyze the data we have seen nothing out of the ordinary for the past ten to fifteen years.

So, we know that we are in an active cycle with more storms and stronger storms. The big question is, are there man made changes to hurricanes? This is an important question because over time we are changing the chemical balance of the atmosphere. We know that we are adding more carbon dioxide and more methane which is going to warm things up. The next question is, by how much?? Some of the most credible scientists say anywhere from a small amount to a moderate amount. It is open for debate. There is no absolute answer. Hurricanes are simply heat engines. As bad as they can be, they have a function, to release stored heat in the tropics. If we did not have hurricanes we would probably have something worse! Here is where it gets complicated. How will a few degrees rise in sea surface temperature affect the intensity of hurricanes, keeping in mind that there is a lot more to the intensity of hurricanes than simply sea surface temperature. I have read research and have discussed this with my colleagues from the National Hurricane Center who say that even a doubling of carbon dioxide in the atmosphere by the year 2100 would result in only a 5-10% increase in both the intensity and rainfall from hurricanes. Certainly not enough to make a huge impact. Keep in mind that during the middle of the 21st century we will be reverting to the quiet part of the mulitdecadal-scale fluctuation of hurricane activity. This debate will continue as the reality is, the atmosphere is extremely complex and ever changing.

I am not a big fan of long range forecasts. Don't get me started on the hurricane pre -season forecasts. However, there is one long range forecast which I generally trust. We watch water temperatures in the Pacific closely. Sea surface temperatures in the equatorial Pacific play a major role in the positioning of the winter jet stream. During an El Nino winter (warmer than normal water temps in the Pacific) the jet stream moves inland over the southwest and eventually moves over the Gulf of Mexico and near Florida. This brings frequent rain and storms to the sothwest and southeast. The opposite, or La Nina, is occuring now. The Pacific waters are cool and the jet stream is moving inland over the pacific northwest. This is resulting in storms in Oregon and Washington along with heavy snows inland. The jet stream is far removed from Florida, so we are left with mild and generally dry weather. Even during a La Nina winter we can experience an occasional cold front with some rain and strong storms but more often than not, we will have a quiet winter.

Here is a great link that is updated every Monday.  It gives an overview of the current ENSO cycle and analyzes whether we are experiencing  La Nina, El Nino, or neutral conditions.

  http://www.cpc.ncep.noaa.gov/products/analysis_mo
nitoring/lanina/enso_evolution-status-fcsts-web.pdf

By far, the number one e-mail topic that makes it into my in mail box at paul.dellegatto@foxtv.com is "TELL ME WHY IT RAINS EVERYWHERE BUT AT MY HOUSE?!!!" It is a great question. We are in the rainy season, so why won't it rain??

The simple answer. Bad luck!  Allow me to explain. We all know that Florida rainfall in the summer comes mainly in the form of  thunderstorms. The problem begins that on a good day, only about 40% to maybe 50% of the area will receive the afternoon thunderstorms. Summer rainfall here by definition is erratic and not evenly distributed. Think about it, rainfall across most of the country is generated by areas of low pressuer moving along the jet stream. Here, the rainfall mechanism is local gulf, land, and lake breezes. Where the local winds intersect during a given day is where the rainfall is going to fall. Granted there is a general pattern where the east coast seabreeze usually meets the west coast sea breeze, somewhere along I-75. Sometimes, the west wind will dominate and storms that try to develop near the coast don't really get cranked up until they are far inland leaving the beaches high and dry. This pattern can last for weeks. Last summer, the seabreeze lined up from near Citrus Park in Hillsborough County all the way south to central Sarasota county. Tampa International Airport was one of the areas that got nailed with summer rain to the point that rainall there in 2007 was several inches above normal. Yes, the official reporting station had more rain than normal while 10 miles east of TIA, a full fledged DROUGHT was underway. That folks, is Florida rain! What usually happens is that over time, rainfall usually evens out. It may not be days, it may not be weeks, but eventually rainfall totals approach normals everywhere. It sure is frustrating to see your lawn dry up and your water bill go up, but this is our climate, and it is perfectly normal.

I also hear from viewers who tell me that they have been living here all of their lives and how they remember when they were a child it would rain every day at 4pm. A couple of things. Yearly rainfall normals have fallen slightly over the years so that may be part of it. More importantly, if it did rain at your house at 4pm, then about 60% to 70% of the area did not get rain at 4pm because the average rainfall coverage here is about 30% to 40% in the afternoon.

Let me know how you are doing so far this rainy season. I know parts of Pinellas, Manatee and Sarasota counties have struggled. Let's all hope that the rain we do get the rest of the year is from thunderstorms and not hurricanes!!

As a follow up to my earlier post. We are rapidly approcahing "prime time" when it comes to hurricane season. A few things our weather team will be watching.

1) Water temps in the Atlantic, Caribbean, and the Gulf of Mexico.

So far, temps are near normal across across most of the Atlantic and above normal in the western Carribean and the Gulf of Mexico. Obviously, above normal water temps in these areas is not good for Florida and the entire Gulf coast.

2) Upper level winds/steering currents

For the past few months the upper level wind pattern has been similar to that of the '06 season. Strong shear and a trough along the east coast of the US is not conducive to a major hurricane hit. However, most computer models are showing a pattern chance in a week to ten days that will be much more favorable for tropical development south or east of us. Steering current winds are impossible to forecast more thatn about 7-10 days out so we have no idea how they will be positioned during the most active time of the season.

3) Dust from Africa.

We are learning that the amount of dust blowing off the continent of Africa has a significant impact on the number of storms that develop. So far we have seen lots of sand and dust on satellite and that is good.

On a side note, we are in the midst of a weather pattern change here in Central Florida. We have seen a west wind pattern for over a week, which lasted a lot longer than usual. High pressure is slowly sliding north so the summer rains should start developing closer to the west coast. We have seen signs of this taking place this afternoon and this pattern should continue each afternoon at least thru Wednesday.

It was good to see that the situation in Coral Gables has finally resolved itself. As i am sure you have heard, Bill Proenza has been "reassigned" while deputy drector Ed Rappaport has been named interim director of the National Hurricane Center. What hurt Bill was that he was considered an "outsider". Yes, he was a long time employee for the National Weather Service but  he was not part of the inner circle of the Hurricane Center. He overplayed the role of the Quicksat sattelite. Yes, it needs to be replaced but his comments that forecasts could be 16% less accurate were a stretch. I am sure there are issues to be addressed but he had the offseason to deal with them. The public deserves a sense of control and assurance from the National Hurricane Center, not one of disorganization and infighting.

Strange summer weather so far. The Bermuda high has been struggling to establish itself in the normal summer time position. the main weather feature so far this summer has been an east coast trough. Dry air aloft and subsidence is going to result in below normal rain chances and above normal temperatures for most of this week. By the way, if the east coast trough remains in place for the rest of the summer then the chances of a major hurricane hit from the Atlantic will be reduced!

Thank you to everyone for submitting their weather pics. All of the information for our contest is on the link below. It is a great umbrella.

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