How do subtropical and tropical storms differ? Lehigh Valley residents may soon be asking
- The National Hurricane Center highlighted an area of potential development along the southeastern United States this week
- The system could move north or northwest, bringing widespread rainfall
- We should expect further improvements to the forecast in the coming days
BETHLEHEM, Pennsylvania – What’s the difference between a subtropical and tropical storm?
Lehigh Valley residents may be interested in the answer to that question this week, as the long-range forecast calls for a system to impact the area by the end of the week.
“Despite the potential subtropical storm designation, it’s just rain here” if the storm arrives, EPAWA meteorologist Bobby Martrich said via text message Monday. “But it can be an appropriate amount at first.”
In his video forecast Monday, Martrich noted that the National Hurricane Center had highlighted an area of potential development across the southeastern coast of the United States.
EPAWA’s forecast for 9/18 and next week, covering:
■ Timing of the cold front/rain showers today
■ Track several consecutive dry days this week
■ Watching a coastal/subtropical depression this weekend https://t.co/ucMPyL6p7I
-Bobby Martrich | Epawa (@epawawx) September 18, 2023
By 11 a.m. Monday, there was a 30% chance of tornadoes forming over a seven-day period. According to the NHC, the system “could gain some subtropical characteristics this weekend if it remains offshore while slowly moving toward the north or northwest.”
Tropical versus subtropical
The biggest differences between tropical and subtropical storms are in the way they form and in their broad impacts.
Tropical storms are areas of low pressure fed by warm waters in the Gulf and along the southern coast. The warm water helps power the storm, with the heaviest rain being closest to the center. These storms usually have a smaller wind field.
Subtropical storms are also areas of low pressure, but it’s the warm waters and temperature changes that help save energy. These storms usually experience heavy rainfall far from the center, and the wind field usually expands to a greater distance from the center of circulation.
The most important thing to remember, according to the National Weather Service, is that tropical systems have the potential to quickly become hurricanes, while subtropical storms do not.
However, if a subtropical storm remains over warm waters long enough, it may eventually become fully tropical.
How much rain can we get?
Meteorologists say it’s too early to answer that question, but rain could spread throughout Saturday, Saturday night and Sunday if things come together.
The latest forecast discussion from the NWS forecast office in Mount Holly, New Jersey, said several model solutions bring widespread rain to the area by late Saturday, continuing into Sunday.
“Expect further improvement to the forecast as this remains in the 6-7 day range, but it should be noted that the overall trend looks wetter in our area,” the discussion said.
“There are also some indications that the system could benefit from tropical moisture which means rainfall amounts could eventually be significant.”
One thing to watch for that will determine the possibility of a subtropical designation, Martrich said, is the amount of time the system spends over the warm waters of the Gulf Stream late in the week.
(tags for translation) Lehigh Valley Weather