We begin another day with clear skies and temps for most of us in the 70s.
Look for another mostly clear to partly cloudy day. It is expected to be a little bit warmer today, with highs averaging in the mid-90s...and east winds around 5-to-10 mph.
Tonight should be partly cloudy...lows in the mid-70s...and light winds.
The tropical depression in the Gulf is now forecast to move slightly farther north than earlier expected. This has the potential to bring some rain into south/southeast Alabama in the Thursday to midday Friday time frame. So, some of our far southeastern counties could be affected by some showers from this system. The rest of us should remain dry throughout the rest of our 7-day forecast.
A slow moving frontal boundary that is helping to steer this tropical system away from us is also expected to bring us cooler, drier air by the week's end. Instead of highs in the 90s, look for highs in the upper 80s by week's end and going into midweek next week...lows should drop into the 60s.
Skies should be mostly clear throughout the extended holiday weekend and into next week.
Have a nice hump day!
Mickey Ferguson, WBRC First Alert weather
FIRST ALERT UPDATE: The tropical system over the Gulf of Mexico is becoming better organized this morning and there is a good chance this will be a named Tropical Storm very soon. The water in the Gulf of Mexico is plenty warm and this will continue to fuel the developing tropical system, which may become a high end tropical storm or hurricane by landfall. We’re still anticipating a north and northeast turn tomorrow and the system will be on track to make a landfall along the Gulf Coast of Florida late Thursday. Over the next two days the system will churn up the Gulf with a risk of rip currents that will include the Alabama Gulf Coast.
So the question remains, where will landfall occur? There is a model spread that includes areas as far west as Panama City, and areas east to Tampa. I’m thinking the more likely landfall point will be in the Big Bend area of Florida, east of Apalachicola. The system should cross Florida quickly with improving weather just in time for Labor Day weekend.
WHAT CAN WE EXPECT: The tropical system, in a more indirect way, will help provide some humidity relief in the longer range forecast. However, we will have no major impacts based on the current forecast track. In fact, most areas will remain dry through the rest of the week. We could see a stray afternoon shower or storm today, tomorrow, and possibly on Thursday. Otherwise, look for periods of sunshine with highs in the 90s. The easterly breeze is helping out, especially in the shaded areas! The breezy weather will likely continue through the end of the week as the tropical system passes to our south.
THE WEEKEND: An east to northeast flow will remain in place this weekend as the tropical system races out into the Atlantic. This should bring us a refreshing break in the mugginess across the area. Highs will be in the 80s, with lows in the mid 60s by Sunday morning. The weekend will also be dry, with sunny weather lingering into next week.
COLLEGE FOOTBALL: Tide fans traveling to Texas can expect dry weather for Saturday, with highs nearing 90° for the outdoor tailgate. Auburn fans may have a stray shower or storm in the area Saturday afternoon. Otherwise, the forecast looks mostly dry for the evening game.
OTHER TROPICAL DEVELOPMENTS: Tropical storm warnings are in effect for the Outer Banks of North Carolina. TD#8 could soon become a tropical storm and this system will impact the region today and tonight. Hurricane Gaston remains over the central Atlantic and continues to move away from the United States. I am watching another tropical wave over the far eastern Atlantic near Africa. This system could become better organized as it enters the western Atlantic in about 5 days. We’ll keep you posted!
We begin another morning under clear skies with very mild temps. As of the 3am hour it was 79-degrees at the Birmingham airport.
Today should bring us another sunny, hot day across Alabama. Expect highs in our area to average near 93-degrees...east winds at 5-10...and only about a 10-percent chance of a brief shower.
Tonight should see mostly clear skies...lows near 73...and light winds.
Tropical depression number-9 continues to churn in the Gulf with 35 mph sustained winds. This system is moving to the west at around 7mph. TD-9 still has the potential to become a tropical storm as it is expected to make a turn to the north and northeast. The forecast trek still takes this system across the big bend area of Florida sometime on Thursday. With this scenario Alabama is not expected to be impacted by this system.
A frontal boundary will give us a slight chance of rain on Thursday and help to steer the tropical system away from Alabama.
Cooler temps and dry air are expected for Friday into early next week.
Mickey Ferguson, WBRC First Alert weather
This is the 2nd in a series of 5 blog posts on hurricanes. You can click here for the first one. This blog will concentrate on the atmospheric dynamics behind hurricane formation and intensification.
Most hurricanes begin as "tropical disturbances", or organized groups of thunderstorms in the tropics that last for at least 12-24 hours. To understand how these groups of thunderstorms organize into a tropical depression or tropical storm, we must first examine three neat atmospheric processes: latent heat, surface pressure, and wind balancing.
1. Latent heat
It takes energy to evaporate water. Think about when you get out of a warm swimming pool on a warm day. The water temperature may be 87 degrees, and the air temeprature may be 87 degrees, but if the wind is blowing when you get out of the pool, it feels cold to you until the water dries off your skin. Same when you get out of the shower. The energy used to evaporate the water is called latent heat, and it has to come from somewhere, so it comes from the cooling of the water on your skin. That energy is now in that water vapor though, so if it condenses back to liquid water, the energy will be released in the form of heat. This is called latent heat. Latent heat is released when water is condensed from water vapor into liquid water.
So, when a thunderstorm forms and air parcels rise through the atmosphere, they may initially cool, but once their dewpoint is reached and water starts condensing, especially in a moist tropical atmosphere, latent heat is released, warming the atmosphere. Often, the release of latent heat by normal thunderstorms in tropical regions may warm the upper levels of the atmosphere by 5 to 10 degrees F. In hurricanes, it can be more than 20 degrees F, as we will see below.
2. Surface pressure
The air pressure exerted by the atmosphere at the ground (or ocean) surface is basically equal to the weight of all air molecules above that point. That's why pressure decreases with height, and baseballs go a lot farther when hit by the Colorado Rockies at home than by the LA Dodgers.
The density of the air is equal to the mass (weight) of each cubic foot of air. Cold air is more dense than warm air, so when the air warms aloft, it lowers the air density, and therefore it lowers the weight of the air in each cubic foot. Reducing the weight of the air at any level above the surface lowers the surface pressure, as less weight is pushing down on the ground/ocean.
This is a cross-section (east is to the right, up is up) of temperature (compared to normal) through Hurricane Katrina in 2005. These temperature departures are in degrees C. Near the center of the storm, temperatures aloft are 25 degrees F above normal, and 15-20 degrees warmer than they are just 100 miles to the east or west. It is this very warm air aloft in a hurricane that causes the low pressure at the surface.
3. Wind balance
There are several forces that push air around in the atmosphere to produce wind. The three main ones involved in a tropical storm are the pressure gradient (air tends to flow from high to low pressure), the Coriolis force (air is accelerated toward the right in the Northern Hemisphere), and the centrifugal force (air gets thrown outward from the center of circulation).
So, if an organized area of thunderstorms in the tropics produces enough warm air aloft, surface pressures can drop, and a surface low can form. Air initially tries to flow toward the low pressure, but it is deflected to the right by the Coriolis force, as shown below.
Initially, the air flows directly toward the low pressure in the center. But, with time, the Coriolis force deflects the wind to the right. In a tropical storm, the wind still blows with a component toward the center, but it is deflected to the right enough to cause a counterclockwise rotation. In most non-tropical weather systems, the winds become completely in balance with the Coriolis force, known as geostrophic balance.
4. Bringing it all together - the feedback loop
If an area of low pressure forms due to the warming aloft produced by a tropical disturbance, and there is not too much wind shear (winds aloft to tilt the storms with height, causing the heat and associated surface low pressure to be spread out), wind will start blowing in toward the low pressure in a counterclockwise fashion, (see the diagram above). If the ocean water is warm enough (usually over about 80 F), the air converging into the low pressure area can cause more and bigger storms to form, br bringing in a larger volume of moist air from around the initial storms, and because when air converges near the ocean surface, it tends to rise (it can't go down into the water). These bigger storms then release more latent heat, further lowering the pressure at the surface, forming a tropical depression, and if the water is warm enough, eventually a tropical storm. This is the feedback loop getting going.
The bigger storms caused by the pooling of moisture and lifting due to convergence release more heat aloft and produce lower surface pressures. The lower surface pressures lead to a stronger pressure gradient, and therefore stronger winds. The stronger winds then lead to more convergence of moisture, more big storms, more heat release, and even lower pressures. Once the winds get strong (well into tropical storm range, at least 50 or 60 mph), waves in the ocean get bigger, and researchers suggest that warm sea spray gets blown into the air, providing an additional source of warmth aloft as it is carried upward in the storms around the center. If the water is warm enough and the feedback loop continues, a hurricane will be present.
The low pressure in the center of a hurricane is always strongest at the surface, and decreases in intensity with height, because as you go up, there is less warm air above you to cause low pressure. Once a hurricane becomes strong enough and the low pressure at the surface gets deep enough, air starts sinking due to the extreme low pressure at the surface relative to the pressure aloft. This sinking air actually dries up some of the clouds in the middle, producing the eye of the hurricane. Also, in organized tropical storms and hurricanes, the thunderstorms tend to orient in spiral bands around the center, with areas of descending air between them, as shown above.
The picture below is of Hurricane Ivan in 2004, and was taken from the International Space Station at an oblique angle. Notice the spiral bands and the taller thunderstorms near the eye.
Blog 3 will be out later this week, and will discuss hurricane effects (winds, storm surge, flooding rains, tornadoes).
Dr. Tim Coleman
Here are the first college football kickoff forecasts of the 2016 season. While Alabama will be playing indoors, conditions for the tailgate will be hot and steamy.
Still a small chance for a pop-up afternoon shower or storm in Auburn on Saturday. Most of the day will be dry, with pleasant weather for game time.
WBRC First Alert Meteorologist Wes Wyatt
Tropical depression nine, centered in the SE Gulf of Mexico, appears to be more organized this afternoon to me, as thunderstorms are starting to develop near to the weak center of circulation. USAF hurricane hunters found no winds of tropical storm force in their flight this morning, but it would not be surprising at all if this system becomes a tropical storm before the end of the day, with wind shear backing off allowing the storms over the center. These storms allow the upper-level heating and subsequent pressure falls at the surface that lead to intensification.
However, the system will encounter shear again within 48 hours, and the National Hurricane Center does not expect it to become a hurricane before making landfall in northern Florida late this week. In addition, NHC expects the storm to be steered eastward by a weak cool front that will bring drier air and cooler nights to Alabama by the weekend.
The hurricane hunter aircraft will investigate the system again this afternoon, and then we will know if it is a tropical storm. If the NHC track is correct, the system would not affect the Alabama and NW Florida beaches too much, other than to bring some scattered thunderstorms and brisk north winds late this week. Here in Birmingham, we could see a pick-up in afternoon storms Thu and Fri, then a beautiful Labor Day Weekend with lower humidity. But, a small number of computer models take the storm farther west, so all that could change. Everyone with interests along the Gulf Coast should keep an eye on this system.
We will have updates here on the blog, and then on Fox 6 news at 5:00 pm.
I will publish part 2 of my series on hurricanes this afternoon on the blog around 4:00 pm. This blog will explain the dynamics of how hurricanes form, why they sometimes intensify and sometimes do not, why wind shear affects them, etc.
Dr. Tim Coleman
FIRST ALERT UPDATE: At the time of this update, Tropical Depression #9 was centered about 170 miles west-southwest of Key West, Florida. The system is moving west at a slow 7mph and some additional strengthening is possible this afternoon and evening. The system may become tropical storm Hermine or Ian. Most of the dynamical model data shows a northeast turn towards the Big Bend Area of Florida on Wednesday, as a cold front approaches the region. Right now the cone of uncertainty track includes areas as far west as Panama City, FL and as far east as Tampa, FL. The primary impacts from a landfall will likely occur on Thursday and possibly linger into Friday. As the system approaches the Gulf Coast, the chance for scattered showers and storms will increase for places like Destin and Panama City on Wednesday and Thursday. Based on the current forecast track, the heaviest rain (6”+ totals) will impact the Florida Peninsula. If you are traveling to the coast for Labor Day weekend, you can expect improving weather beginning on Friday.
LOCAL IMPACTS: Based on the latest forecast for TD#9, I’m expecting minimal impacts across our part of the state. In fact, we will have mostly dry weather through the remainder of the week. A few isolated pop-up showers and storms may develop later today in the easterly flow. Highs this afternoon will be in the low to mid 90s. We will have more sunshine for the next few days and it may be a bit breezy at times, with only a stray shower or two late. As the tropical system passes to our southeast, a drier flow will take over. This will set the stage for lots of sunshine and less muggy weather for Saturday and Sunday. Highs will be in the 80s this weekend!
GASTON & TD8: We’re expecting Tropical Depression #8 to near the Outer Banks of North Carolina tomorrow night as possibly a tropical storm. The system is also expected to turn north and then northeast over the Atlantic. So a direct landfall is not expected. Gaston remains a powerful Hurricane over the central Atlantic. This system is now drifting north at 2mph and is not expected to change direction and move west. You can get the latest tropical tracks on our First Alert Weather App. I will also have updates beginning at Noon on WBRC.
WBRC First Alert Meteorologist Wes Wyatt
The main focus of the weather across the south is a tropical depression that has formed in the Gulf of Mexico. TD-9 could become a tropical storm later today. While it appears Florida will experience the brunt of the wind and rain from this system, the forecast trek could change over the coming days. We will closely be monitoring this system.
We begin our day with clear to partly cloudy skies.
Expect highs today to top out in the low to mid 90s this afternoon under mostly sunny to partly cloudy skies. We only have a slight chance of a brief heat-activated shower or two.
Tonight should be mostly clear...lows in the mid-70s...and light winds.
The extended forecast looks to be about the same as today...partly cloudy with highs in the mid-90s...along with a slight chance of an afternoon shower.
Rain chances made need to be increased later in the week, depending on what happens with the tropical system in the Gulf.
Mickey Ferguson, WBRC First Alert weather
WHERE WILL IT GO? We expect the system to move northwest towards the central Gulf and then begin a sharper turn north and northeast by Thursday. The Florida Gulf coast looks to be the more likely location for a landfall, although areas as far west as Gulf Shores will need to remain weather alert for any possible changes in track.
WHAT ABOUT TIMING? The impacts involving heavier rain could begin as early as Wednesday and linger into Friday. So if you have Labor Day weekend plans, the primary threat for rain and gusty winds along the Gulf Coast would impact Thursday and Friday, with improving weather on Saturday.
NEW DEVELOPMENTS: We are also monitoring a new tropical depression near the Carolinas. This system is expected to turn north as it approaches the Outer Banks of North Carolina on Tuesday. By then the system may be a tropical storm. The next name on the 2016 list is Hermine. We’re also keeping an eye on Category Three Hurricane Gaston over the central Atlantic. The latest satellite data shows a well defined eye as the system drifts very slowly northwest and remains well away from land.
THE LATEST ON OUR FORECAST: The bigger weather story here at home will continue to be hot and humid weather through Wednesday. Keep the shades handy because we will have lots of sunshine over the coming days, with a few stray showers, and possibly an afternoon storm. Feels-like temperatures will be surging into the triple digit range. Based on the latest thoughts regarding TD#9, I’m thinking deeper tropical moisture to the south could spark a better coverage of scattered showers and storms on Thursday. Drier air could begin to work in behind the tropical system on Friday and help set the stage for a very nice weekend. Right now I’m forecasting sunshine, with highs in the 80s and lower humidity for Saturday and Sunday. We will continue to fine tune the forecast and Mickey will be in with more updates beginning at 4AM.
WBRC First Alert Meteorologist Wes Wyatt