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GPM overpass of Hurricane Delta

GPM Captures Hurricane Delta on Approach to the Gulf Coast

The 2020 Atlantic hurricane season will go down as one of the most active seasons on record, currently second only to the incredible 2005 season in terms of the number of named storms.  The 2020 season is only the second time in recorded history (the other being 2005) that the Greek alphabet has been used because the number of named storms has exceeded the number of regular names on the list.  Another interesting aspect of the 2020 season has been the number of storms that have struck the northern Gulf Coast. So it is no surprise that the latest storm, Hurricane Delta, would also find its way to the middle of the northern Gulf Coast.

Delta began as a tropical wave moving from the eastern Caribbean into the central Caribbean. In response to increased thunderstorm activity, a low pressure centered formed south of Jamaica on the evening of October 4th, becoming the 26th tropical depression of the season or TD#26. As TD#26 continued westward it became better organized, and on the morning of the 5th was named Tropical Storm Delta. Being a small storm, Delta responded quickly to the favorable environment of very warm waters and almost no wind shear, and became a hurricane later that same day just 12 hours after becoming a tropical storm. Delta continued to strengthen overnight, and early on the morning of the 6th had become a Category 2 hurricane. Delta then continued to rapidly intensify, and just six hours later it was a Category 3 storm, before being quickly updated to a Category 4 hurricane less than an hour after that by the National Hurricane Center (NHC).  Later that afternoon Delta’s maximum sustained winds had increased to a reported 145 mph by NHC as the storm continued moving through the western Caribbean headed for the Yucatan Peninsula.  By late evening however, Delta began to lose some strength, and was down to a Category 2 storm when it made landfall the next morning around 5:30 am CDT near Puerto Morelos on the Yucatan Peninsula.  Delta moved steadily northwest across the northeastern tip of the Yucatan and by late morning on the 7th was already emerging back over the open waters of the southern Gulf of Mexico.  

Having been disrupted by its transect over land, it took some time for Delta to re-organize over the Gulf, and it wasn’t until the evening of October 7th that Delta’s central pressure actually began to fall again. By now the steering currents affecting Delta were also changing.  As Delta neared the western edge of the subtropical ridge that had been steering it generally westward, an upper-level trough moved into Texas; these two changes caused Delta to recurve towards the north over the western Gulf of Mexico.  During the early morning hours of Thursday October 8th, Delta’s winds responded to the somewhat lower central pressure, and the storm again reached Category 2 intensity with sustained winds of 100 mph.  Throughout the rest of the day, the central pressure continued to come down, and by 4pm CDT, NHC reported that Delta was once again a Category 3 storm with maximum sustained winds of 115 mph.  

Video file

It was at around this time that Hurricane Delta was overflown by the NASA/JAXA GPM Core Observatory satellite - at 00:41 UTC October 9th (7:41 pm CDT Thursday October 8th) as shown in the above animation.  Here, rainfall rates derived directly from the GPM Microwave Imager (GMI) and Dual-Frequency Precipitation Radar (DPR) provide a detailed look into Delta, which at the time was a Category 3 hurricane located about 300 miles south of the Louisiana coast, with sustained winds reported at 115 mph by the NHC. GPM clearly shows a well-defined eye with an eyewall wrapping completely around the center of circulation.  Heavy rain rates (shown in red and pink) within the eyewall also nearly completely wrap around the center.  Both are characteristic of a strong, well-developed circulation. Heavy rain rates also extend north and northeast of the center, while outer rainbands are already pushing inland.  Delta would go on to reach its second peak intensity overnight, with sustained winds of 120 mph as it headed for the coast of Louisiana.

As Delta approached the coast of Louisiana on the morning of the 9th, it finally began to weaken as a result of increasing southwesterly wind shear, cooler ocean temperatures and its proximity to land.  Delta eventually made landfall near Creole, Louisiana around 6pm CDT as a Category 2 storm with maximum sustained winds of 100 mph, not far from where powerful Hurricane Laura made landfall near the end August. By helping to reduce windshear across the Caribbean and tropical Atlantic, the ongoing La Niña event in the Pacific has most certainly contributed to the large number of storms in the 2020 Atlantic hurricane season.  

Credits:

Story by Steve Lang (NASA GSFC)
Animation by by Alex Kekesi and Greg Shirah (NASA Goddard Scientific Visualization Studio)