Drier Air Dictates The Forecast for Florida and 93L

Drier air is filtering in to a lot of places this evening. For most of us east of the Rockies, this is a good thing….and I am not just talking about here in Florida. Dry air has also leached into 93L today, which is good news so far for the northern Lesser Antilles.

Let’s start in Florida tonight where the unseasonable cold front is moving through the Big Bend Region:

072914 FL Front

Record lows could occur tonight in north Florida as the drier air moves in. Drier air allows for enhanced radiational cooling. This along with some cooler air from the north, temperatures there should fall into the mid to upper 60s except for right along the warmer gulf waters. The real change across the northern half of Florida will be the drier air that will certainly make it feel cooler than it has been. Feels like temperatures in Tallahassee and in surrounding cities have been 108°F or more in recent days. In the next couple of days, feels like temperatures could be as much as 20 degrees cooler as dew points could be low enough that the air could feel like the actual temperatures.

For central Florida, it will take another day before this drier air truly moves in with dew points in the upper 60s and lower 70s. The below meteogram from IA State for Tampa shows that the dew points could fall as far as the mid 60s there, but this seems a bit generous. I think the actual low dew point in Central Florida tomorrow night or Thursday morning will fall between the NWS (in green) and the model avg forecasts (in white)…or into the mid-upper 60s. South Florida low dew points should be on Thursday morning in the low 70s.

072914 DP TPA

Is Dry Air Killing 93L?

In short, no. Dry air has gotten entrenched into the eastern and northern side of what I actually think is tropical depression #3. I’ll be using the two terms, 93L and TD3 interchangeably here, but please refer to the NHC for official information. As I said yesterday on twitter, I do believe this system became a tropical depression last night as a closed, although slightly elliptical, center and abundant thunderstorm activity became apparent. Unfortunately, when dry air reached 93L’s center this morning that thunderstorm activity became limited. 93L currently resides on the line between a tropical cyclone and a tropical wave.

The road ahead of 93L is a tough one due to dry air, slightly cooler water and high shear. The next 4-5 days carry the danger of dissipation if any of the aforementioned factors become overwhelming.  These factors should keep this system less intense. Current reliable models keep what still should become Bertha as a weak tropical storm as it approaches the Lesser Antilles.

 

Cross section of the HWRF 18Z run for 93L at 24 hours. Abundant dry air can be seen above 500 mb (18,000 ft) intruding through the center.

Cross section of the HWRF 18Z run for 93L at 24 hours. Abundant dry air can be seen above 500 mb (18,000 ft) intruding through the center. From Tropical Tidbits.

 

The current spaghetti models bring this system toward the central or northern Lesser Antilles in about 4 days (Friday or Saturday). As discussed above, I do not think this will be able to become more than a moderate tropical storm especially if it is flirting with land. The grand scheme of the forecast is that 93L will be moving around the edge of the Bermuda High at the surface and between two ULL features aloft. How much latitude is gained over the next week will be dictated by how strong the system becomes. A weaker system will be located farther from the Bermuda High, and a stronger system will be located closer to the Bermuda High and thus farther north. The current trend is for a weaker system that will track farther south and west.

072914 93L Pasta

In some ways, this trend is a friend in more ways than one. Many locations in the eastern Caribbean are in a slight and worsening drought. Roughly 10% of Puerto Rico is under drought, and more than half of that island are abnormally dry. Rainfall from 93L could prove to be good for these islands if the system is weaker as it moves through. I do want to mention that there is NO correlation between weaker systems and beneficial effects, but with this system and in this condition it could be beneficial for the islands.

 

072914 PR Drought

 

After 5 days, we could see a period of intensification if this system is still alive. This is in part due to warmer ocean temperatures and a favorable pattern aloft for thunderstorms to grow.

 

As always, I’ll be watching.

–Jonathan, @JonathanBelles

New Tropical Depression Likely Soon

The tropics continue to simmer this Monday, and the convection oven is turning up. A great deal of organization has occurred today in the disturbance in the east Atlantic. So much so that the disturbance was tagged as Invest 93L. The hurricane models are now running, and a possible recon mission is planned for Thursday. As was expected, this system is doing better than tropical depression #2.

 

072814 93L Loop

There are two main reasons why I believe 93L is doing better than TD2:

  1. 93L is much larger in size than TD2. This extension of influence allows the circulation of 93L to fend off the dry air that ended up evaporating TD2. The farther reaching clouds act as a buffer system for the core of this future cyclone, especially in direction of movement. See how far away the drier air is from 93L in the water vapor below
  2. Like TD2, this system has a Kelvin Wave passing over it over the next day, and these Kelvin Waves often beef up tropical cyclones in the 48 hours following their passage. Wait! What is a Kelvin Wave? See this week’s Meteorology Mumbo at the top right of this page!

072814 93L WV

 

The Latest TWO From The NHC: 

072814 93L TWO 8pm

The Models And Why I Think These Chances Are Too Low

This morning’s ASCAT pass had somewhat removed westerly winds, which are generally a sign of cyclogenesis. At that latitude, winds are generally coming from the opposite direction or from the east. Although this ASCAT pass does not conclusively show a closed center, but satellite imagery has shown an improvement in organization today. The thunderstorm activity requirement needed to be a cyclone has been checked off for quite some time, and the closed center requirement is very close to being checked off as well. My guess is that this will be checked off overnight if we get another ASCAT pass or additional bursts of thunderstorm activity. Earlier microwave imagery actually showed some curved rain bands, which are more typical of tropical storms.

072814 93L ASCAT

Will 93L Meet TD2’s Demise?

Possibly. The latest models, which I will discuss more in depth in the days to come, are showing a large area of high wind shear as this system reaches the Lesser Antilles on Thursday or Friday. An interesting idea is that the GFS had today is that the anticyclone that builds atop strong tropical systems could split that zone of high shear into two distinct zones. An additional reason that this system could weaken is that cooler waters closer to the northeastern Lesser Antilles could get in the way. After 3 days, this amount of confidence going into the forecast falls just a bit. Here’s what the current models say…surprisingly without mention of the cooler water and higher shear.

072814 93L 18z intensity models

072814 93L 18z track models

 

Models are generally trending (our friend) toward the west just a tad. I do think that the intense intensity models will come down as they start to see the higher shear and cooler waters. In the longer term, I do think that the Antilles will get some much needed rainfall from what will likely be Bertha. I expect this pot to continue to bubble and convection to stay steady overnight.

Let’s keep the conversation going on Twitter @JonathanBelles

Thanks for reading!

–Jonathan

Abnormal Cold Front To Reach Florida as the MDR Moistens

Although the weather this afternoon is comparatively quiet (albeit dangerously warm in the panhandle) in Florida, the troughing pattern that has been with us on the east coast for a few weeks is about to bring down an unseasonably strong cold front.  The Storm Prediction Center had initially issued a summertime Moderate Risk of severe weather for the central Appalachians into this evening for the system coming out of Canada. In their latest update, they have outlined a reduced but still enhanced risk for much of the area. That same front could produce severe weather tomorrow from the coastal Carolinas to southern Mississippi. It is not surprising that a rare front could produce severe weather. In Florida, we don’t even need a front to receive severe weather as seen by the EF1 tornado on the space coast recently.

How far south with the front go? 

The Weather Prediction Center has had this front dipping as far south as the Cape Coral to Lake Okeechobee area, but their most recent forecast halts southern motion across Interstate 4. Below is the current WPC/GFS Depiction:

WPC/GFS Depiction on Thursday morning. Dew points are shaded. Lifted index is contoured.

WPC/GFS Depiction on Thursday morning. Dew points are shaded. Lifted index is contoured.

Interesting in the above graphic is that dew points could fall below 65 along the spine of the state, but also the lifted index is positive. A positive LI generally means sinking air. This depiction is for the morning time, so storms probably would not be prevalent anyway, but it is interesting nonetheless. This may keep storms down on Thursday, but given that dry air aloft is already keeping storm chances down this week you probably won’t notice too much of a difference.

How Low Could Dew Points Go?

The general trend is that the farther south you are, the less impact there will be and the impacts will be later. As we saw with the last front (which only made it to Tallahassee), impacts could be seen 100 miles south of this front, which shows up well in south Florida and on the map above. I have chosen three sites to plot on meteograms, and GFS (in blue) picks up the dip in dew points well. Tallahassee could again have a dew point in the mid 50s on Thursday Morning. GFS has Tampa dew points dipping into a more comfortable range for quite some time late week, and dew points in the 60s even into south Florida on Friday. It is interesting to note that the NWS (in green) is not really biting on these lower dew points, but I don’t blame them. Some of these drops could be almost historic…especially in Tallahassee. Confidence is high that dew points will drop as this front approaches.

072714 DP Meteograms

 

Any cooler air coming?

Probably not. Temperatures north of I-4 could drop a couple of degrees, and there is a subtle lowering in high temperatures toward the end of the week. The cool factor will come mostly from the drop in humidity. Confidence in this is in the low category due to the lack of the entire model suite at that time, the irregularity of the event, and the normal variability in cloud cover during the summer. Up to the north? Yes, this will drop temperatures for 2/3rds of the country!

Temperature Anomalies from the GFS on Thursday Morning. In celcius, but the take away from this is that blue/purple is cooler than average air.

Temperature Anomalies from the GFS on Thursday Morning. In Celsius, but the take away from this is that blue/purple is cooler than average air.

Long term temperature forecast for early August. Again, cooler than normal in blue.

Long term temperature forecast for early August. Again, cooler than normal in blue. From the CPC.

 

You say more active tropics, will this front spawn anything?

As of right this second…no. That is not to say that this pattern will not spawn a homebrew system in the weeks to come.  Pressures are expected to be lower than normal due to the troughing pattern, and with fronts lingering in the area we have a ‘kick’ for something to develop on in a similar way that Arthur did.

There is something to talk about in the Tropics right now, and it comes from the MDR.

072714 TWO 2pm

 

This system has a slightly better development chance than TD2 did because the air ahead of this disturbance is slightly more moist, however shear is considerably higher now. Tracking of this system is difficult due to the lack of any organization, but organization is expected to become better in the days to come. Current models bring this system (as a vorticity maximum) toward the central or northern leeward islands. I’ll be keeping my eye on this and the rest of the tropics all week.

For more frequent updates, follow me on twitter @JonathanBelles! Send me questions too!

Remember, if you have to take your kids to the store or anywhere else…put your phone in the backseat so that you have to retrieve it when you get to your destination. This way, you will not forget your kids in the hot car AND you won’t be texting or talking on the phone while you are driving. Turn your ring tone to something fun so that if your phone does ring, your kids can dance!

Until next time,

–Jonathan

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