Tropical Depression Ten (2020)

Storm Active: July 31-August 1

On July 29, a tropical wave moved off Africa, but unlike its predecessors, made little westward progress. Almost immediately, the system had a pronounced spin, but there was little thunderstorm activity north of the center. The disturbance drifted north-northwestward over the next few days and gradually became more organized. With a new flare up of central convection, the system became Tropical Depression Ten east of the Cape Verde islands.

Overnight, the depression made its closest approach to the islands, but it was small enough that it brought only a few showers to the easternmost part of Cape Verde. By August 1, the system was encountering cooler water and more stable air. Thunderstorm activity waned and the shallow system turned left toward the west. That night, the depression dissipated.

The above images shows the exposed center of Tropical Depression Ten on July 31 with a bit of thunderstorm activity off to the west-northwest.

Tropical Depression Ten was small and short-lived; it did not affect land.

Hurricane Isaias (2020)

Storm Active: July 29-August 4

On July 23, a large tropical wave exited Africa. It was perhaps the first of the season to really punch a hole in the dry Saharan air layer (SAL) to its north. The disturbance passed south of the Cape Verde Islands and pushed rapidly westward. Within a few days, the wave had a huge area of vorticity associated with it, but was highly disorganized. It's often the case that larger systems take longer to consolidate, and this was no exception. Though it developed a broad low pressure center, no well-defined center of circulation appeared for several days. At its fast clip, the outer rain bands of the tropical wave began to affect Barbados by July 28. By that time, tropical storm force winds were already occurring to the north of the center.

Overnight, the low passed over the Windward Islands at a remarkable 25 mph clip, bringing strong wind and heavy rains to nearly all the Lesser Antilles during that period due to its large size. As far as internal dynamics were concerned, the system was still struggling. Instead of a well-defined center of circulation, there was only a sharp trough axis oriented southwest to northeast, with competing mid-level vortices and convection clusters at each end. The large-scale cyclonic spin helped to turn the axis toward south to north on the 29th, but the system was still a mess on satellite imagery. It was only that evening that a new central area of thunderstorm activity formed atop a clear center and Tropical Storm Isaias was born, already packing 50 mph sustained winds. Not only did Isaias become the new earliest "I" storm (previous record-holder: Irene of 2005, which was named on August 7), but it also brought the number of named storms in July 2020 to 5, also tying an Atlantic record held by 2005.

Beginning later that day, the storm brought significant flooding and mudslides to Puerto Rico, the Dominican Republic, and some of the surrounding isles. The low-level center soon made landfall along the southern coast of the Dominican Republic, but the overall circulation was so large that the land encounter did not significantly disrupt the system. In fact, at the same time, a mid-level circulation moving east to west parallel to the northern coast became better defined. Soon, the surface center reformed under the nascent vortex and strengthening resumed. This is not to say interaction with Hispaniola did not affect Isaias at all: the central overcast became a bit separated from the eastern and southern portions of the circulation by a few tongues of drier air. Nevertheless, the detached bands pulled an immense amount of tropical moisture northward into the storm that fueled intense thunderstorms as well as the system's further development.

Overnight, Isaias moved northwestward into the Bahamas and strengthened into a category 1 hurricane. Some struggles with dry air caused the storm to level off in intensity on the 31st. Overnight, it peaked in intensity with 85 mph winds. The minimum pressure was 987 mb. Meanwhile, it continued northwestward at a fairly quick speed under the continuing influence of the neighboring subtropical ridge. During the morning of August 1, Isaias's center passed directly over Andros Island; around the same time, dry air, pushed into the circulation by upper-level winds out of the southwest, completely overcame the storm. A totally exposed center of circulation moved west-northwestward off of the island and nearly all convection was left on the other side of a north-south wall of low-humidity air. This caused Isaias to weaken back to a tropical storm that afternoon.

The storm continued to battle back, however, and convection blossomed again that evening. This sort of fluctuation continued, though less extreme, through the next few days. The shear persisted throughout and Isaias was not quick vertically stacked even thunderstorm activity was on the upswing: the mid-level center remained east of the low-level one. Fortunately for Florida, the system moved north-northwestward paralleling the coastline, and shear meant that the west half of the circulation was almost dry. Impacts to the state were confirmed to a few bad squalls. Late on August 2, the storm began to accelerate northward as it felt a cold front approach the U.S. east coast.

During the day of August 3, the interaction of the front with Isaias changed the shape of the storm: it took on the characteristic comma shape of a cyclone entering the mid-latitudes and the heaviest rainfall now fell northwest of the center. The outer bands of Isaias swept across South Carolina through the evening as the center approached. The inner core also recovered a bit from the latest intrusion of dry air and managed to build a more complete eyewall on radar. This resulted in the storm regaining hurricane strength.

Baroclinic forces (which are the mechanism by which non-tropical systems strengthen) also contributed to the intensification of Isaias: an anomalous jet stream out of the south fed unusually strong winds into the cyclone's eastern side a few thousand feet above ground. This phenomenon slowed the storm's weakening during and after landfall. Moreover, some of the winds mixed down to ground level, bumping up Isaias's intensity and matching its peak of 85 mph winds and a pressure of 988 mb. It maintained this through landfall just north of the Carolina border just before midnight. Isaias joined Bertha, Cristobal, Fay, and Hanna to become the earliest fifth named storm landfall in the United States on record.

By this time, the storm had begun to accelerate in earnest. On August 4, its forward speed exceeded 30 mph toward the north-northeast and it weakened back to a tropical storm. Nevertheless, rainfall totals of 3-6 inches (with isolated higher totals) were common along the storm track through the Carolinas and up the mid-Atlantic though Virginia, inland Maryland, and eastern Pennsylvania. Sporadic tornadoes broke out on the system's east side nearer to the coast. Isaias moved over the interior northeast and became post-tropical that evening. The remnant system brought rain and wind as far north as southern Quebec before dissipating.

The above image shows Isaias after achieving hurricane status for the first time on July 31st.

After moving across the tropical Atlantic as a tropical wave for nearly a week, Isaias was finally named in the Caribbean.

Hurricane Hanna (2020)

Storm Active: July 22-27

During the third week of July, a tropical wave moving through the Caribbean began to exhibit thunderstorm activity near its northern end over the Greater Antilles. Due to land interaction and wind shear, the disturbance did not develop further for the next few days. Around July 21, a broad surface low formed in the Florida straits, bring scattered storms to much of the eastern Gulf region and Florida. It slowly consolidated over the next day, ultimately becoming Tropical Depression Eight late on July 22.

A ridge over the southern U.S. kept the depression moving west-northwestward across the open Gulf of Mexico, though at a slow forward speed. On July 23, Eight's structure improved drastically and the central pressure dropped, but winds lagged behind. It wasn't until late that night that the storm was upgraded to Tropical Storm Hanna. Hanna added to the growing list of records set by its predecessors, becoming the earliest "H" storm. The previous record-holder was Harvey of 2005, which formed on August 3 of that year (not to be confused with the devastating Hurricane Harvey of 2017, which retired the name). At the time of naming, Hanna had vigorous convection in the southern and eastern semicircles, but the northwest struggled some with dry air. This led to the formation of a curious mid-level eye feature, even with the cyclone still a minimal tropical storm! The mid-level center was not yet vertically aligned with the surface circulation due to a bit of wind shear, so Hanna wasn't quite ready to strengthen more rapidly.

On July 24, the storm turned more to the west and filled in more in the northwest quadrant, leading to faster intensification. On top of extremely warm ocean waters, these favorable factors were enough to boost Hanna to hurricane status by the morning of July 25. By that time, tropical storm conditions were affecting the south Texas coastline, and a large eye became increasingly evident on satellite and radar imagery. Hanna's central pressure dropped steadily through the afternoon despite increasing proximity to land. It reached its peak intensity as a high-end category 1, with 90 mph winds and a central pressure of 973 mb, just before landfall in south Texas.

As it made landfall, Hanna took a dive to the west-southwest, angling towards northern Mexico. It weakened to a tropical storm and soon crossed the international border, but maintained an impressive radar signature throughout the next day. By the afternoon of the 26th, the storm weakened to a tropical depression. The next day it weakened to a remnant low and dissipated over the mountains of northern Mexico.

The above images shows Hanna at landfall in south Texas.

Hanna's slow track through the western Gulf of Mexico allowed it ample time to strengthen into a well-organized category 1 hurricane.

Tropical Storm Gonzalo (2020)

Storm Active: July 21-25

Around July 17, a tropical wave associated with a monsoonal trough of low pressure near the equator entered the Atlantic from the east. To its north, plentiful dust-laden air still streamed westward off of the Saharan desert over the ocean. For the first part of July, this Saharan air layer (SAL) contributed to a very dry tropical Atlantic and stifled the season's early tropical waves. This wave, however, stayed low in latitude and produced persistent shower activity as the trade winds guided it westward.

There was an elongated area of enhanced vorticity associated with the system for a few days, but no single circulation center. Some spin became apparent early on July 20, when a surface low formed. Though the circulation became better defined by the evening, thunderstorm activity was still a bit spotty and winds remained lackluster. The system entrained more moisture from the inter-tropical convergence zone (ITCZ) to the south on July 21, and strengthened a little, earning the designation Tropical Depression Seven late that afternoon. Organization steadily increased overnight, and the storm became Tropical Storm Gonzalo during the morning of July 22. Following in the footsteps of earlier storms of the 2020 season, Gonzalo was the earliest ever seventh named storm, beating out Gert of 2005, which formed July 24 of that year.

The steering pattern near Gonzalo was quite simple: a strong subtropical ridge to its north kept it traversing the 10°N parallel at a gradually increasing speed. Environmental factors were more mixed, however. Ocean temperatures were quite warm and wind shear was fairly low, but the SAL lurked to the north and the system was fighting dry air. That day, Gonzalo lost some of its outer banding features even as the inner core improved and it strengthened some. The small cyclone peaked at 65 mph winds and a pressure of 997 mb that night, but the central dense overcast promptly collapsed a few hours later as dry air invaded Gonzalo. The storm ejected a blob of convection to the west, but the circulation was nearly bare apart from that by the morning of the 23rd, leading to some weakening.

A small shield of thunderstorm activity made a comeback later that day, once again covering the center of circulation, but the weakening trend continued throughout the next couple of days as the central pressure rose. Meanwhile, Gonzalo's westward motion had hastened, making it more difficult for the cyclone to maintain a closed circulation. During the morning of July 25, Gonzalo made landfall in Trinidad as a minimal tropical storm and weakened to a tropical depression shortly after. Land interaction further sealed the cyclone's demise and what was left of the circulation dissipated that afternoon. Though fast moving, Gonzalo brought heavy rain to portions of the southern Windward Islands and northern Venezuela. After dissipation, the remnant tropical wave continued west-northwestward through the eastern Caribbean.

The above images shows Gonzalo over the open tropical Atlantic. Despite warm waters, dry air and stable air eventually overwhelmed the small cyclone.

Gonzalo took an unusually southern track, ultimately affecting South America.

Tropical Storm Fay (2020)

Storm Active: July 9-11

On July 4, a disturbance that had brought heavy downpours to Louisiana dipped southward into the Gulf of Mexico. Though a surface low formed over water, it was weak and moved northeast back over land without any tropical development. Over the next few days, it moved inland across Georgia and South Carolina. By July 8, the broad circulation began to feel the approaching Atlantic waters and generated large areas of thunderstorm activity offshore. By that evening, the system had moved over the ocean just off the border of the Carolinas, but it lacked organization.

The morning of July 9 saw the formation of a surface vortex, but convection still lay off to the northeast of the center, precluding tropical cyclone development. It wasn't until a new center of circulation took over under the thunderstorms near Cape Hatteras that afternoon that the system became organized enough to be classified. Aircraft data indicated the presence of tropical storm force winds east of the center, so the disturbance was designated Tropical Storm Fay. Upon formation, Fay continued the streak of broken records by becoming the earliest "F" storm recorded. The previous record was Tropical Storm Franklin of 2005, which formed on July 21.

While over the northern edge of the Gulf Stream, Fay managed to develop deeper convection that night, resulting in some modest strengthening. Soon, however, the center moved over colder waters and dry air invaded the circulation, displacing thunderstorm activity away from the center to the north or southeast. Fay reached a peak intensity of 60 mph winds and a pressure of 998 mb during the morning of July 10 as it approached the mid-Atlantic coastline. Well before landfall, heavy rains spread across the northeast. That afternoon, the cyclone's center crossed the coast in southern New Jersey. Once inland, Fay decayed rapidly and lost tropical characteristics by early on July 11 over New England. Later that day, the vortex was absorbed by another system approaching from the west.

The above image shows Fay a few hours before landfall in New Jersey. The cyclone had taken on a "hybrid" appearance between tropical and subtropical, with comparatively little cloud cover near the center of circulation.

Fay took a rather unusual track up the east coast: rather then veering east, it moved nearly due northward during its time as a tropical cyclone.

Tropical Storm Edouard (2020)

Storm Active: July 4-6

On July 3, a low pressure system formed along a stationary front northeast of the Bahamas. Though atmospheric conditions were only marginally favorable, the small system managed to organize quickly and become Tropical Depression Five the next morning. Sandwiched between a ridge to the south and a trough to the north, the depression was steered rapidly east-northeastward. Very early on July 5, Five passed Bermuda, making its closest approach just northeast of the island. Thunderstorm activity at the time was minimal, however, so the island experienced little more than gusty winds and showers.

There was a resurgence of deep convection that evening and winds increased to tropical storm force, prompting the naming of Tropical Storm Edouard. With this upgrade, Edouard became the earliest "E" storm ever in the Atlantic, surpassing 2005's Hurricane Emily, which was named on July 11. The cyclone did not have much time as a tropical storm, however, as it accelerated northeast and began extratropical transition on July 6. By late that afternoon, the still vigorous system had merged with a nearby frontal boundary roughly 500 miles southeast of Newfoundland.

Edouard was a fast-moving and short-lived storm that took a typical track northeastward across the subtropical Atlantic.

The above image shows the track of Edouard, including the progress of its extratropical remnant across the ocean toward Europe.