Tropical Storm Dolly (2020)

Storm Active: June 22-24

On June 19, a non-tropical low pressure system formed off the southeastern United States. Initially, wind shear in the area was high enough to stifle any development. The system moved steadily northeast over the next few days and became better defined. During the day of the 21st, an area of convection popped up near the center, but was still disorganized. Atmospheric conditions improved some more the next day as the low moved closer to a tongue of warm ocean waters from the Gulf Stream. Later on the 22nd, the disturbance was classified Subtropical Depression Four several hundred miles east of the mid-Atlantic coastline.

The depression moved east-northeastward away from land at a moderate pace over the next day and crossed over the warmest ocean waters to be found at that latitude. As it did so, thunderstorm activity increased near the center and a curved banding feature set up in the northern semicircle, fanning eastward. By the afternoon of June 23, the cyclone had a more concentrated wind field with values in excess of gale force. Thus, it was upgraded to Tropical Storm Dolly. Its bout of strengthening was short-lived, however, for on its track lay the much colder waters of the open north Atlantic. Dolly's satellite presentation quickly degraded overnight and the storm weakened to a tropical depression on June 24. Later that morning, it became post-tropical well southeast of Nova Scotia. The remnant low picked up speed toward the northeast until it dissipated a few days later.

This image shows Dolly just after being classified as a tropical storm.

Dolly was a short-lived tropical storm that did not affect any land areas.

Tropical Storm Cristobal (2020)

Storm Active: June 1-9

During the last week of May, a central American gyre (CAG) set up over the southeastern Mexico, Guatemala, Belize, and the surrounding ocean areas. CAGs are broad areas of low pressure and enhanced rainfall, which clearly exhibit cyclonic rotation on satellite imagery. They are akin to monsoonal lows in other parts of the world, and typically occur near the beginning and end of hurricane season. Often, the rotation and ample moisture of CAGs can lead to tropical cyclone genesis in neighboring bodies of water. In this case, a disturbance embedded in the CAG developed into a tropical depression in the Eastern Pacific on May 30. The next day, it strengthened into Tropical Storm Amanda and made landfall along the Pacific coast of Guatemala. By that afternoon, the circulation had dissipated over the mountainous terrain.

Nevertheless, locally heavy rainfall had been occurring in the region for several days and continued as the remnants of Amanda moved inland. Flooding displaced many from their homes as over 10 inches of rain fell in some mountainous areas of Guatemala. Very early on June 1, a new convective outburst formed, unusually, over the southern half of the Yucatan peninsula. The new disturbance already had some spin to it, and further development occurred rapidly when as it moved westward into the Bay of Campeche that afternoon. Just a few hours later, it was classified Tropical Depression Three.

The depression was initially very broad, with little to mark its center of circulation on infrared satellite imagery. That night, it took some steps toward constructing a central dense overcast and gradually organized. On June 2, the cyclone strengthened into Tropical Storm Cristobal and broke the record for the earliest a third named storm had ever formed in an Atlantic hurricane season. The previous title-holder was Tropical Storm Colin in 2016. Cristobal was still embedded in the CAG and faced a strong ridge to its north, so it moved little that day, actually diving south toward the Mexican coastline that evening. Some strengthening occurred overnight and the cyclone reached an intensity of 60 mph maximum winds and a pressure of 994 mb before sliding slowly southeast across the coast of southern Mexico during the morning of June 3.

Since the storm did not move far inland, weakening was slow and flooding widespread over the areas that had already experienced rains for several days. Cristobal weakened to a tropical depression on June 4 and the center crossed the border into northwestern Guatemala. A weakness in the ridge over the Gulf states opened at last that night, causing the storm to turn northward. Cristobal traversed the spine of the Yucatan during the day on June 5 and recovered strength with more of the circulation over water. Nevertheless, land interaction had taken its toll; the circulation was broader and more asymmetric, with significant dry air entrainment on the southwestern side, a single (though powerful) curved band of convection to the north and east, and little to no activity near the center of circulation itself. The cyclone regained tropical storm status and entered the Gulf of Mexico early that evening.

Rainfall finally abated in Mexico as Cristobal moved northward, but storm totals exceeded 20 inches in regions bordering the Bay of Campeche. The storm strengthened modestly on June 6, but its structure was far too broad (with some subtropical characteristics) to allow rapid intensification. Its immense eastern band of thunderstorms swept across the coast of west Florida that evening, despite the fact that the center of circulation was near the center of the Gulf, 400 miles away! Cristobal's look became a bit more tropical the next day as the center approached the Gulf coast, with moderate convection popping up near the center. Maximum winds were near 50 mph when the center made landfall in southeastern Louisiana during the afternoon of June 7; at the same time, central pressure reached a minimum value of 992 mb. The large circulation brought measurable storm surge to a large swath of coastline stretching eastward to west Florida, with the worst impacts just east of the point of landfall.

Cristobal weakened to a tropical depression overnight but continued to bring heavy rain and tropical moisture northward. A trailing band lingering over coastal Louisiana brought some of the most severe storms to the region nearly a day after actual landfall as the center of circulation accelerated into Arkansas. Unusually, the system maintained tropical status throughout June 9 as it passed over Missouri and along the border of Iowa and Illinois and even entered Wisconsin before becoming extratropical that evening. The extratropical remnants merged with a front some time after.

The above image shows Cristobal just before its first landfall along the Bay of Campeche.

Taking into account the CAG that spawned Cristobal and the storm itself, southern Mexico was affected by flooding rains for nearly a week.