11:45 AM (Monday) | ***Slow-moving Tropical Storm Sally to reach hurricane status and produce substantial rainfall amounts in the northern Gulf coastal region over the next couple of days***
Paul Dorian
Gravity waves can be seen on this satellite image pushing radially outward from the inner core of Tropical Storm Sally during an intense burst of deep convection. This type of activity is indicative of rapid intensification and Sally is quite likely to reach hurricane status later in the day. Image courtesy “windy.com”, MJVentrice, Twitter, NOAA
Overview
There are currently five systems in the Atlantic Basin that are characterized as tropical depression or greater and that high number hasn’t happened since September of 1971. Currently, there are three systems that are classified as tropical storms, Sally, Teddy and Vicky, and one hurricane, Paulette, which passed over the island of Bermuda earlier today. Tropical Storm Sally is a slow-moving system now over the northern Gulf of Mexico and it may end up producing up to two feet of rain during the next couple of days in portions of the northern Gulf coastal region. After landfall, the remnants of Tropical Storm Sally are likely to push to the north into southern Mississippi and then to the northeast through Alabama and Georgia – bringing some heavy rainfall along its path. The heaviest of the rain from Sally’s remains are likely to stay south of the Mid-Atlantic region as a strong cold front barrels from northwest-to-southeast towards the eastern seaboard. That cold front will usher in the coolest air mass of the season so far in the Mid-Atlantic region and Northeast US during the upcoming weekend.
A healthy looking Tropical Storm Sally at mid-day Monday appears to be on the verge of forming an “eye” in this IR satellite image and quite likely will attain hurricane status later today. Images courtesy College of DuPage, NOAA
Details
The very active 2020 Atlantic Basin tropical season continues…There are currently four named storms in the Atlantic Basin (TS Sally, TS Teddy, TS Vicky, Hurricane Paulette) of tropical storm status or greater and that last happened in September of 2018 when Florence, Helene , Isaac and Joyce were on the map at the same time. There are currently five tropical systems that are classified as tropical depression or greater and that hasn’t happened since September of 1971 when six systems were on the map at the same time (Edith, Fern, Ginger, Unnamed, Heidi and Irene). All of these very active occasions (2020, 2018, 1971) took place in the same “climatological peak” time period for the Atlantic Basin tropical season of the middle of September. (Credit for this historical information on tropical activity to Dr. Philip Klotzbach, Colorado State University, Twitter).
Rainfall amounts in the northern Gulf coastal region will be excessive over the next couple of days as Tropical Storm Sally slowly grinds its way through the region. Some spots could receive up to two feet of rainfall by mid-week. Map courtesy NOAA/WPC
Tropical Storm Sally looks very healthy on satellite imagery at mid-day with an intense burst of deep convection as it grinds its way to the west-northwest at only 6 mph and features maximum sustained winds of 65 mph. This system appears to be in the early stages of developing an “eye” and it is quite likely to intensify into hurricane status later in the day as it is in a favorable environment of low wind shear – perhaps even as high as category 2 or 3. This deep burst of convection earlier in the day generated gravity waves that pushed radially outward from the inner core of Tropical Storm Sally and this event was captured well by satellite imagery (top).
The mid-day map of the Atlantic Basin features three tropical storms (Sally, Teddy and Vicky) and one hurricane, Paulette, which is now pulling away from the island of Bermuda. The last time there were four systems of tropical storm status or greater was September of 2018. Map courtesy NOAA/NHC
Whether “major” hurricane status is actually reached or not, Sally will become a significant rain producer in the region from southeastern Louisiana to the western part of Florida’s Panhandle over the next couple of days. In fact, some spots could receive as much as two feet of rain as Sally painfully inches its way through the region as a result of a general weakness in the overall wind field. It is not all that unusual for a tropical system to slow down at this particular latitude (i.e., near 30 degrees North) as this is a region that can feature a weakness in the overall wind field with tropical trade winds (easterlies) to its south and the “westerlies” to the north. Indeed, Hurricane Harvey stalled out a few years ago right around the same general latitude causing tremendous rainfall amounts in places like Houston, Texas over a several day period.
The coolest air mass of the season so far will push into the Mid-Atlantic/Northeast US at week’s end following the passage of a strong cold frontal system. Map courtesy NOAA, tropicaltidbits.com
After landfall on Tuesday in extreme southeastern Louisiana or southern Mississippi, Sally is likely to push slowly to the north into central Mississippi and then turn to the northeast and go through Alabama and Georgia before likely ending up in the Carolinas at the end of the week. At the same time, strong high pressure will be pushing over the southern part of Canadian anchoring a very chilly air mass for this time of year. At the leading edge of this chilly air mass will be a strong cold front that will be barreling towards the eastern seaboard late in the week in a northwest-to-southeast fashion. This approaching front is going to reduce the chances for heavy rainfall from Sally’s remains to make it as far north as the Mid-Atlantic region, but there certainly can still be some shower activity. Following the passage of the strong cold front, the coolest air of the season will flood the Mid-Atlantic and Northeast US bringing the lowest temperatures of the season so far. In fact, high temperatures on Saturday are likely to be confined to the 60’s in the DC-to-Philly-to-NYC corridor which is well below-normal for this time of year.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
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