By: Al Kaprielian – Oct. 2015
Our warm weather of September is now just a memory. Boston saw its first heat wave in September since 1983. A heat wave is defined as three or more consecutive days when the temperature reaches 90 degrees or higher. An upper level ridge of HIGH PRESSURE was responsible for the hot and dry days we saw in September. As October began, the upper level ridge weakened and moved farther into the Atlantic Ocean.
A cold front brought heavy rain for the last day of September. This heavy rain caused major flooding on area roadways with some cars stuck in flood waters. The cold front was not only responsible for the heavy rain but brought an end to our warm and humid weather.
Next, our attention was focused on Hurricane Joaquin which battered the Bahamas with heavy rain and strong winds.
It first looked like Joaquin would make landfall on the east coast around North Carolina or the mid-Atlantic region. Joaquin became a category four hurricane on the saffir-simpson scale.
A category five is the highest and worst case hurricane. Joaquin had maximum sustained winds at 130 miles per hour and then weakened slightly to 125 miles per hour as the hurricane moved over San Salvador in the Bahamas.
Later on Friday October 2nd, Joaquin started to make the turn to the northeast which would take the hurricane away from the Bahamas and the US.
On Saturday October 3rd, hurricane Joaquin started to regain power and by noon on Saturday maximum sustained winds had reached 155 miles per hour, which is a strong category four hurricane.
Fortunately, Joaquin is moving away from the US. The next target for the hurricane is Bermuda which looks to be impacted on Sunday, October 4. The very warm ocean waters off the Bahamas caused Joaquin to strengthen into a category three and four hurricane. Hurricanes get their energy from very warm ocean waters that are over 80 degrees.
By Thursday October 1st, we started to see the majority of our computer models shift Joaquin farther east offshore. This eastward shift in the track, spared the east coast of a devastating hit.
Why did the majority of the computer models shift the hurricane farther east?
There are a couple of reasons. First, it looked like an upper level low pressure system over the southeast US would capture Joaquin and cause it to hook west and into North Carolina or the Mid-Atlantic region. In the end, the upper level low pressure never captured Joaquin.
Why?
One reason is that the distance between the upper level low and Joaquin was too large for the upper low to capture the hurricane. Also there was another low pressure air mass ocer the Atlantic Ocean. It seemed like this low pressure air moved above Joaquin and the counterclockwise circulation around this low pressure air cause Joaquin to be steered to the northeast. As a result of this, the track was shifted more east and offshore of the US east coast.
The European model (ECMWF) is one of our better computer models. This model was consistent all along from one run to the next, in taking Joaquin more eastward and out to sea. The majority of the other computer models were showing the hurricane tracking into North Carolina and the mid-Atlantic region. By Thursday, October 1st, most (not all) of the other computer models started agreeing with the European model. The European model was the first computer model that brought hurricane Sandy up the east coast form the tropics. Hurricane sandy moved into New Jersey and caused a lot of damage and destruction. Luckily this time New Jersey and the east coast was spared from a major hurricane. The differences in the computer models as to the track of a hurricane or even a winter storm makes forecasting the weather a challenge. This is why you should check the weather forecast each day because computer models can change from day to day.
Even though we feel relieved missing hurricane Joaquin, historic flooding occurred across South Carolina. Lots of roads in the Charleston, South Carolina were under water. These areas saw over a foot of rain. This rain was caused by a low pressure system (not Joaquin), and a stationary front. Stationary fronts can cause heavy rain. The heavy rain was enhanced by tropical moisture coming in off the Atlantic ocean. With strong high pressure over Canada and lower pressure to the south this causes a strong pressure gradient (lots of wind). Strong winds caused trees and power lines to come down in South Carolina causing power outages. There were also some power outages in eastern MA near the coast due to the strong winds. With strong winds along the coast and high Astronomical high tides coastal flooding occurred from New England all the way down the east coast. As we move into the week of October 5 the weather will begin to calm down with lots of sun and warmer temperatures. Also with the strong Northeast winds diminishing this will end the coasting flooding situation. Enjoy Fall!!
Before I close one last mention of Joaquin. The track of the hurricane passed close enough to Bermuda to cause heavy rain (flooding) and strong damaging winds (Power Outages) later Sunday & Sunday night October 4.