TWO TYPES OF WATERSPOUTS

It is not often we see waterspouts in Jacksonville.  Well today I think we had the most famous waterspout in Jacksonville history. Over 50 of you sent us pictures and the waterspout seemed poised for the sky cameras as it slowly moved north over the river today.  Waterspouts typically are located in the waterspout capital of the world, the Florida Keys.  The Keys provide a perfect environment for an average of 400 waterspouts every year.  Jacksonville's balmy, hot, and humid weather was just like the islands.

Light winds made for favorable waterspout conditions.  Outflow boundaries from previous thunderstorms moves east from the I-75 area and collided with the east coast sea breeze resulting in severe storms with 1" hail and lightning which struck a home on fire near Normandy on the Westside.  As the storms moved north from Putnam and St. Johns county, the perfect placement of the river underneath provided an ideal location for the waterspout.  Fortunately the long length of the river was the reason why the waterspout never moved ashore.  Typically they have a lifespan of only 15 minutes.


There are two types of waterspouts and fortunately we had the weaker non-tornadic waterspout variety.   The other, tornadic waterspouts, begin as true tornadoes over land in association with a thunderstorm, and then move out over the water. They can be large and are capable of considerable destruction. What we had was a fair weather waterspout. They form only over open water. They develop at the surface  and climb up in association with warm water temperatures and high humidity in the lowest several thousand feet of the atmosphere. They are usually small, relatively brief, and less dangerous. The fair weather variety of waterspout is much more common than the tornadic.  Needless to say it was scary for everyone today.  Thanks everyone for all the great photos you emailed.

GETTING HOT THIS WEEK

The hottest month in Jacksonville is July. Temperatures most days in the month are 90 degrees or higher. The end of July begins the start of summer and First Coast locals always sweat out hot afternoons waiting for cooling thunderstorms. In fact, over a 30 year average of July months, 23 days are above 89 degrees.   

Get ready for a return to ninety's all week long into next week. June is often a scorcher.  In 2008, June had 21 days at 90 or above.  That was also the hottest month out of the '08 summer.  The average for 90 degree days in June is 16.  The onset to this upcoming heat wave is due to a lack of forecasted rain and a ridge of high pressure in the Gulf.

The 500 mb ridge in the Gulf results in sinking air over Jacksonville which suppresses thunderstorms.  The blue vectors show NW winds around the right side of the Gulf ridge.  
Looks like the pool or river will be the best places to cool off.

DOPPLER ANALYSIS

On Thursday evening a Mesoscale convective complex (MCC) rolled eastward from the Panhandle and raced into Lake City and into Northeast Florida.  A MCC is a thunderstorm complex that has specific characteristics.  This storm which brought over 1-2 inches of rain overnight is typical of a MCC.  They are nocturnal, last at least 6 hours and the size of the cloud tops are at least 62,000 miles with temperatures measured by a satellite of -26 F or colder. 

These pictures show the storm before it reached Jacksonville when it was in the Panhandle. The top two images are base reflectivity from the Tallahassee WSR-88D Doppler radar site. A bowing section of the thunderstorm is approaching St. Marks at 6:40 pm indicating strong mid level air dropping down to the surface due the denser cooler outflow.  This gust at the surface spreads out and bows the cell radar signature on the radar.


Twenty minutes later the storms rapid eastward movement is shown in the second picture entering Taylor county.  The cell was moving east at 60 mph.


The last picture is the radial velocity product  that clearly shows  the downdraft moving away from the radar site in red and yellow.  The greens are winds moving into the storm in relation to the WSR-88D's location.  Notice the moist strong winds coming in off Apalachicola Bay.  This fueled the thunderstorms and they remained severe when they blew into the First Coast. 

Wave Masking Makes For A Sneaker Swell

It was impressive to see chest high clean swell on our beaches Thursday. An offshore gale kicked seas up to 23' off the mid Atlantic and some of it sneaked into our breaks. It is rare to get powerful waves with offshore winds in Jacksonville. I thought the surf would of been much smaller but the swell was big enough to resist attenuation by the west winds that gusted over 30 mph. Sometimes offshore winds will knock the surf flat. In retrospect, a look at the models shows why the surf stayed up. Above the WW3 period chart clearly show an impressive 15-16 second swell hitting Florida and the Bahamas in yellow. The blue is a separate 5-6 second windswell moving northeast due to the WSW winds. The 2 dimensional graphics masks out the underlying groundswell.

Above is a look at only the new windswell period. It would of been totally flat here if it weren't for the groundswell running against the northeast moving windswell.

A graphical version of actual wave observations at the St. Augustine buoy confirms two separate swells. You can see the graph of wave energy with the period at the top and energy measured at the left. This information shows two wave groups. The largest peak is the new windswell at 6.5 seconds and the groundswell is indicated at 15 seconds. When looking at wave models they only show swells with the most energy. In this example it would be the windswell since its energy is higher. A forecaster could totally miss predicting the groundswell without confirming this spectral density data. Unfortunately this happens often since there are so few buoys off our coast.

A CHRISTMAS WARM SPELL

After weathering record cold in October and November, December has had above normal temperatures and the long term forecast does not show any cool down this week.  A small drop into the 60s is expected at the start ofChristmas week but we should warm back up into the 70s by Christmas.  


The map at the right is a hemispheric view of equal pressure levels around 18,000 feet or 500 millibars.  It  is displaying the average position height of 500 mb above the earth through December 26.  This is the height at the bottom layer of the Jet Stream. It gives us an idea of warm and cold air movements from across the globe.  These teleconnections give advance warning to cold air outbreaks.  But for now, I don't see any freezes reaching Florida anytime soon.  Notice how a ridge sits over Florida with above normal heights in the southeast.  Lower than normal values over California will set the stage for wet and cooler weather in the west. 

The ridge will keep it mildly warm and humid in Jacksonville and redirect any rainy systems around the southeast.  You can see above the rainfall forecast from the HPC and how we stay dry under the ridge.

OCEANIC LOWS GIVE US WIND

Two separate areas of low
pressure in the Atlantic are helping to give us windy weather. Gust's to gale force have occurred in the offshore water's and a satellite fly-over measured winds at 50 kts or 58 mph near the northern low. The QuickSCAT satellite can compute the winds speed based by measuring the water's surface roughness. Wind barbs point in the direction the wind is flowing with the tail or flag pointed in the direction the wind is coming from. A flag represents 50 kts and one full barb is 10 kts. A half barb is five knots.

The increase in wind is due to the areas of low pressure combining with high pressure over New England. Air is squeezed between the two pressure systems resulting in high wind. The MRF model run shows the wind turning north over Jacksonville and then west Friday as the low moves into South Carolina. The second low can be tracked as it moves away from Hispaniola and heads north between Bermuda and the east coast. This second low will move into New England this weekend which will result in locally lighter winds here Saturday and Sunday.

ACTIVE WEATHER WEEKEND

Saturday will be wet all day as a surface low moves over north Florida. A short wave over Mexico developed a gale center in the SW Gulf Friday and it will travel into North Florida steered by a strong subtropical jet stream. This is the 3rd set up we have seen recently of cyclogenesis in the Gulf. Typically we would see activity like this during an El Nino winter and not during our La Nina cycle.



The skies clear out Sunday and a front drops in cooling us off with a light inland freeze Sunday and Monday mornings. Strong northeast winds crank Monday due to the 1042 mb high pressure ridge over the mid-Atlantic.

FIRST FREEZE FOR THE SEASON CONFIRMED

Saturday morning the forecasted freeze came true. Here is a list of lows:
Jacksonville JIA 30
Waycross: 27
Nahunta:26
Alma:28
Stark:32
St. Augustine Lighthouse:42
JAX Beach:40
Hastings:35
Glenn st. Mary:29
Gainesville:28
Fernandina Beach:36

WHEN DOES IT FREEZE AROUND HERE?

Jacksonville's average first freeze is December 8th and typically the last freeze is February 18th.
Last year December 9th was the first freeze of the season. Will we have one earlier this year? It's in the forecast and we will find out Saturday morning.

If we reach 32 degrees tonight at the airport it will be several weeks earlier than last year. So far this winter the coldest temperature at the Jacksonville airport was 39 on November 9th. Most lows have been in the 40s and 50s. But a quick shot of cold will last just one night before a warm up with milder temperatures through Thanksgiving. Here is a list of the first dates of temperatures at or below 32 degrees in 2006. Notice how St. Augustine almost got through the whole season without a freeze.

FREEZE WATCH FOR JAX

Here comes another blast of Canadian air which brings the coldest air of the season Saturday morning. I have been watching the temps drop upstream where afternoon highs were in the 30s and 40s over Tennessee Thursday afternoon.

The surface analysis at right shows the surface high parked over Texas and Oklahoma. Remember the wind flows clockwise around this anticyclone so Florida sits on the right side in the patch of cold air flowing out of Canada. The blue isobars are packed closely from the Great Lakes to Georgia and North Florida. Winds flow parallel to the isobars resulting in cold air advection. This horizontal movement of air is hitting us tonight and highs Friday will only reach the low 60s during the day.

The jet stream is dipping south rushing the cold our way. A freeze watch is up for most of the Jacksonville area for Friday night and Saturday morning. This will be the only night for frost during this forecast period. It is so cold that snow has been falling in the southern Appalachian Mountains. The red circles are isotachs marking streaks of faster flowing air. Those jet streaks are converging in the dip that is bending back over north Georgia. This is analogous to cars slowing up at a red light. Traffic backs up. But when the air at 30,000 feet backs up it sinks downward. This confluence is why you will see no clouds in the sky Friday and Saturday. The cold moderates quickly Sunday afternoon and no freeze is expected Sunday morning.