It’s that time of Autumn again, where weather enthusiasts start looking into the longer range forecasts for telleconnections, pattern changes, and the first chance of snowfall; while everyone else who dreads winter will start shopping for new coats, boots and shovels. For now, it’s snow haters rejoice: It appears there will be very little wintry weather through most, if not all, of November.
Warm and moist air, which settled into the region on Wednesday Night, has been scoured out thanks to a cold frontal passage on Thursday afternoon. Sunny and warm conditions prevailed, thanks to lingering warm air near the surface, but temperatures in both the mid and low levels of the atmosphere will cool further overnight. Westerly winds took over for the southerly winds which had dominated beforehand, and will help to usher in the cooler airmass.
This trend will continue through Friday, with cooler air arriving throughout the Northeast United States. Highs will be several degrees colder than they were on Thursday. The air will feel crisp and, well, Autumn-like, with high temperatures topping out in the mid to upper 50’s with a westerly wind component.
The interaction between tropical moisture — remnants of Hurricane Patricia — and a strong mid level atmospheric disturbance over the North Central US will aid in the development of steady rain on Wednesday. As forcing for precipitation increases during the morning hours, steady rains will develop from southwest to northeast throughout the area. Atmospheric moisture content will increase throughout the day, as a psuedo-warm front moves through New Jersey and New York.
Precipitable water values between 200 and 300 percent above average are a testament to the tropical moisture involved in Wednesday’s rains. During the late morning and afternoon, a low level jet stream is expected to strengthen, further aiding in the potential for heavy rains. While heavy rain isn’t expected to be constant, sporadic heavy rains could cause localized flooding, despite the moderate drought conditions in much of Northern New Jersey, New York and Connecticut.
Nearly three years since Hurricane Sandy, many of her visual scars have faded. The memories of the storm, for many, have not. Meteorologically, Sandy remains just as incredible now as she was then — an unbelievable display of atmospheric power. One of the most fascinating aspects of Sandy was how strong she was, despite entering cooler waters. The meteorology behind her pressure is powerful and intricate, still, three years later.
Hurricanes have a strong warm core at the surface, weaken with height, and are barotropic — meaning there are no temperature or density gradients in their environment. This means that they are symmetric — their warm core is entirely surrounded by slightly cooler, but still abundantly warm air. The combination leads to hurricanes being vertically stacked (not tilted with height). Thus, hurricanes need warm water and weak upper-level winds in order to strengthen. Strong upper-level winds can choke a hurricane’s outflow channel, and advect in new airmasses of different temperatures — providing temperature gradients that hinder their development.
In further south latitudes, waters tend to be warmer, and the jet stream tends to be weak. As you head further north, however, the water becomes colder and the jet stream strengthens, leading to stronger upper-level winds. This helps to weaken a hurricane’s warm core at the surface, and tilt its vertically stacked structure, weakening the storm. However, as Sandy headed north, she was able to maintain category one hurricane strength with abnormally low pressures and eventually went on to cause widespread devastation. Why?