Winter Wind in Tampa Bay – A Brief but Detailed Analysis

By SailFlow Meteorologist Shea Gibson

On-water meteorological expert and wind forecaster Shea Gibson checks in with his predictions for the conditions in Tampa Bay. For those sailing in this year’s Helly Hansen Sailing World Regatta Series in St. Pete, take note of the patterns and possible impact on racing in February. 

I will start with the good news for winter winds in Tampa Bay: the windy season runs from October to April/May, before the Bermuda high blocking patterns and northeast GoMex high pressures set in for the summer. In short, sailors have a much higher percentage of catching quality breezes this time of year. The real trick is from which direction winds fill in and how long these wind events last. The west-to-east weather traffic driven by Coriolis processes can be rather intense as the polar jet and the subtropical jet compete over the mid-latitudes of the continental U.S. It can be a vicious battle between warm air and cold air, which in turn can create large areas of instability. We have quite a few scenarios that can play out to bring high diversity in various wind fields as a result of this push-pull of the warm air vs the cold air. Deep mid-level or upper-level lows (ULLs) can form over the eastern Gulf of Mexico and create some very messy situations with shifty S-->W winds. The same types of Lows can form over the US interior and drag powerful cold fronts across FL, thus creating a similar situation. We also have large domes of High pressure that form or, at times, stall over the OH Valley. This brings moderate to strong NE/ENE winds. Other directions can come in strong but might blend out faster than those standard northerly and southerly winds. So, in order to put this in perspective, let’s take these various directions of winds that we typically see and break them down. 

We’ll start with the more complex southerly winds that we typically see ahead of cold fronts. There can be any variance with the standard cardinal direction of southerlies, intercardinal SE/SW, and secondary intercardinal SSE/SSW. We have to take two things into account. First are low-level jets (LLJs) strength for overall instability factors, and second are sea surface temperatures. Generally speaking, the stronger the front, the stronger the overall wind speeds. However, higher air temperatures over cooler waters by over 15-20° can cause shallow marine layering or full-on fog if the dewpoint matches the air temperature (higher humidity). In either case, we generally see winds being weaker and underperforming from model forecasts. This is due to the cooler waters holding a thicker, more stable layer and causing this “decoupling” of winds. In this case, we would need low level jets to force as much down to the surface as possible to override the marine layer. This can be accentuated by any GoMex ULLs that develop to force those winds down. With pre-frontal flow, SE winds generally are weaker but can be thermally induced inside the bay, with S being a bit stronger and SSW/SW directions tending to fill in the most – that is, as long as marine layering doesn’t have huge impacts. Basically, the closer the air temps are to the water temps, the better off. Cooler winds flowing overland masses can mix downstream and crank up in isolated areas all around. My saying in the winter is, “Never trust a South wind in the winter unless it has real muscle!” 

Secondly, we’ll move into W and NW winds. These usually are considered post-frontal winds that fill in behind cold fronts due to High pressure to the west or northwest or are part of the wrap-around flow from those ULLs. For post-frontal winds, these W/NW can punch through rather quickly – even just ahead of the front at times. These typically might last a day but will usually fall off that night as the high pressure responsible for it expands east. Or, if the high remains in place and the front stalls just to the east, it can last a bit longer until the pressure gradient eventually relaxes. The other scenario of strong wrap-around W/NW flow involving ULLs can carry a much stronger wind that lasts longer in most cases. Much depends on how fast the low exits to the north or northeast, but the wind field is much wider and expands over the area, even if it is off the Carolina coast. This can eventually become a northerly wind that fades in time. Keep in mind that these might be considered “onshore” for St Pete Beach but offshore inside the cay where the race rings are. That wind can be dirty and jumpy, with lots of ups and downs in the wind field after being ripped up by mechanical features such as trees/buildings. You will want to be as far away from land as you can be to see that fetch settle down where you are sailing. 

Lastly, we will talk about the well-known winter NE/ENE/E flow. As mentioned earlier, we see a good bit of west-to-east traffic in the winter, but we do see several frequent patterns where large domes of High pressure sit over the OH Valley or TN Valley. These large ridges will typically send a backdoor cold front southward across Tampa and just to the south, then park. The pressure gradient builds up behind this front, and we can get a solid NE/ENE flow or a mix of NE/ENE/E. The farther east the high goes, the more likely it is to veer from NE to E and slowly weaken. The more fixed it is to our north, the more locked in and stronger the NE/ENE flow will be. Now we have to remember that NE flow is cooler air aloft sinking down at an angle towards the surface versus a warmer, more horizontal, southerly wind. This means that it is susceptible to thermal decoupling within the warmer land around the bay. We tend to see stronger winds cranking up just after sunrise, weakening by late morning/noon, and returning back up later in the day. This is problematic to races, typically starting around 10 am and finishing around 2 pm. It is very important to know the general timing of these directions, and computer models can really overperform here. There are a few instances where the High can be in the western US, and we see an all-day N/NNE wind, but it is not very common. Conversely, we have also seen the E flow veer SE and develop some thermal coupling in the afternoon, which can be advantageous to the racers. 

I have talked about many scenarios that generate winds, but keep in mind there are many scenarios that can take it away – that’s another article for another day. Be sure to check all models in the model suite. SailFlow has quite a few, including our own in-house high-resolution SF-WRF 2km model that does pretty well in the Tampa area. It helps to understand the local nuances and the types of bay disbursements with winds. Much of what happens in St Pete is thermally induced or thermally reduced, so know the directions and best-case scenarios plan around what type of gear to use. Best wishes on the water this year, and good luck!

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