I have some good news to share tonight about Debby. I also have some not so good news. First, the good….
The deep convection with Debby is really falling off. This means that the strong showers and thunderstorms that drive the heat engine are not functioning too well. You can easily see the void of deep convection in the graphic. The green circle indicates the area where the center is located. Without deep thunderstorm activity near the center, a tropical cyclone cannot thrive. This is important because it means that the storm is not strengthening and may be on a weakening trend. Now I cannot possibly know for sure, but seeing the collapse of the deep convection that was definitely there last night and for a good deal of today is a good sign. Perhaps the GFS’ idea of a sheared, weaker, pulsing convection type storm is really what will pan out. The ECMWF forecast of a deeper, stronger system seems to be fading quickly.
The other issue is heat content. Hurricanes get their energy from the latent heat which is stored in vast quantities in the worlds’ oceans. The deeper the warm water (about 80 degrees F) extends, the more heat content (also called upper ocean heat content) is available. Shallower water tends to hold less heat content and the shallow shelf waters off the eastern parts of the Florida panhandle are notorious hurricane killers due to this lack of energy (see the graphic to the right- the deep blue is low ocean heat content region). I think that the slow movement of Debby is helping to churn up this shallower water, exhausting what little heat content there is; further diminishing Debby’s ability to maintain deep convection.
All of this adds up to the prospect of Debby weakening and not having much of a chance of recovering. This would keep the wind and surge issues to a minimum but the rain is another problem. This is the not so good news part.
Tropical cyclones = rain. That is how they release the heat stored in the oceans. Condensation is a warming process and the release of all that rain also releases heat. This is the very nature of what makes a tropical cyclone tick, so to speak. Unfortunately, too much rain will lead to problems and it looks like the potential exists for a lot of rain for portions of the Florida panhandle and the peninsula. There is no way to know how much rain will fall and where. This all depends on the convection that I mentioned earlier. If rain bands develop, they will drop heavy rain. But those bands can fall apart very quickly too. So the timing and areal coverage of the rain is difficult to forecast. This is why it is important to keep up with what Debby is doing several times per day. The storm is dynamic, it changes. You need to use more than a few resources to keep up with what’s going on. Whether it’s the NWS site (weather.gov) or a commercial outfit such as your local TV station or other website (like us), you will want to know what the rainfall situation is even between the major advisories issued by the NHC. One great resource is the HPC site linked here where you can get detailed precipitation forecasts. The bottom line is that you need to be aware of the fairly quick changes that Debby could bring your specific area. There are numerous ways to do that.
I’ll have more updates throughout the day tomorrow. And for our Client Services subscribers, do not forget, we have a LIVE broadcast each weekday at 2pm ET where I go over detailed graphics LIVE. We also have exclusive use of Stormpulse maps, live chat and other great features that allow you to gain even more info that can help you stay informed.