Tracking Tropical Storm Bertha: the reason behind the messy system
Tropical Storm Bertha made landfall in St. Bernard Parish, Louisiana, earlier today, with maximum sustained winds estimated to be 45 mph, including higher gusts. The interesting thing about this system is that the "storm" characteristic has been on the isolated side, mainly producing isolated cells on land, with a cluster of more organized storms being produced over the ocean, meaning that damaging winds and more localized areas of flooding have been the main concern.
This is because of the same reason that this hurricane season as a whole has been quiet so far, that reason being what is known as wind shear.
Wind shear, simply put, is the change in speed and direction of winds with height, and the larger the difference, the greater the amount of shear is present. Tropical storms and hurricanes are historically known to be very fragile, needing a low amount of wind shear to be present in the area in order to strengthen and maintain strength.
This is because when larger amounts of wind shear are present, it "tilts" the storm, meaning that the warm, rising air and thunderstorms are cut off from the main circulation, disrupting the heat engine that powers the system in the first place. Once that fuel is cut off, the storm begins to fall apart.
Depending on the El Niño Southern Oscillation, the phase ultimately determines how much of this wind shear, on average, is present during the hurricane season, which can either help or hurt the development of tropical storms and hurricanes. El Niño means higher amounts of wind shear in the Atlantic, whereas La Niña means lower amounts of wind shear in the Atlantic.
Currently, we have entered the El Niño phase of this oscillation, and it is expected to strengthen throughout the rest of the year, so this means that more wind shear will be present throughout the rest of the hurricane season.
This can be seen in the example of current Tropical Storm Bertha, where it has been fighting a large difference in wind speed and direction as it has approached the coast. As stronger upper-level northerly winds blow overhead, it tears apart the majority of storm development that could be possible near the center of the storm, exposing and weakening the center of the storm itself. Since this is a weaker storm and hasn't fully matured into a hurricane, it has a harder time sustaining the self-fueling mechanisms to become anything much greater than it already is.
Another thing working against Tropical Storm Bertha is the fact that this upper-level northerly flow is ushering in a lot of dry air. This also plays a role in preventing storms from sustaining themselves, as moisture is important for not only individual storms but also the system as a whole.
As of the 4 PM advisory, Tropical Storm Bertha is moving to the west at 4 mph, with a pressure of 1000 mb and winds at 45 mph. As it continues to move west through Louisiana, it is expected to remain a tropical storm with 45 mph through Thursday morning before dropping to 40 mph as it enters Texas and eventually loses tropical storm strength by early Friday morning as it approaches areas like Austin and San Antonio.
