2020 Atlantic hurricane season

On December 19, 2019, Tropical Storm Risk (TSR), a public consortium consisting of experts on insurance, risk management, and seasonal climate forecasting at University College London, issued an extended-range forecast predicting a slightly above-average hurricane season. In its report, the organization called for 15 named storms, 7 hurricanes, 4 major hurricanes, and an ACE index of 105 units. This forecast was based on the prediction of near-average trade winds and slightly warmer than normal sea surface temperatures (SSTs) across the tropical Atlantic as well as a neutral El Niño–Southern Oscillation (ENSO) phase in the equatorial Pacific.[4] On April 2, 2020, forecasters at Colorado State University echoed predictions of an above-average season, forecasting 16 named storms, 8 hurricanes, 4 major hurricanes, and an ACE index of 150 units. The organization posted significantly heightened probabilities for hurricanes tracking through the Caribbean and hurricanes striking the U.S. coastline.[5] TSR updated their forecast on April 7, predicting 16 named storms, 8 hurricanes, 3 major hurricanes, and an ACE index of 130 units.[6] On April 13, the University of Arizona (UA) predicted a potentially hyperactive hurricane season: 19 named storms, 10 hurricanes, 5 major hurricanes, and accumulated cyclone energy index of 163 units.[7] A similar prediction of 18 named storms, 9 hurricanes, and 4 major hurricanes was released by The Weather Company on April 15.[8] Following that, the North Carolina State University released a similar forecast on April 17, also calling for a possibly hyperactive season with 18–22 named storms, 8–11 hurricanes and 3–5 major hurricanes.[9]

On May 20, Mexico's Servicio Meteorológico Nacional released their forecast for an above-average season with 15–19 named storms, 7–9 hurricanes and 3–4 major hurricanes.[10] The UK Met Office released their outlook that same day, predicting average activity with 13 tropical storms, 7 hurricanes, and 3 major hurricanes expected to develop between June and November 2020. They also predicted an ACE index of around 110 units.[11] NOAA issued their forecast on May 21, calling for a 60% chance of an above-normal season with 13–19 named storms, 6–10 hurricanes, 3–6 major hurricanes, and an ACE index between 110% and 190% of the median. They cited the ongoing warm phase of the Atlantic Multidecadal Oscillation and the expectation of continued ENSO-neutral or even La Niña conditions during the peak of the season as factors that would increase activity.[12]

Tropical storm (SSHWS)
Duration	May 16 – May 19
Peak intensity	60 mph (95 km/h) (1-min)  991 mbar (hPa)

On May 12, the National Hurricane Center noted an area of low pressure was expected to develop over subsequent days northeast of the Bahamas.[17] Early on May 14, the NHC began to monitor an area of shower and thunderstorm activity over the Straits of Florida for development.[18] The system moved generally northeast into the region of the Bahamas while steadily organizing, becoming the season's first tropical depression at 21:00 UTC on May 16.[19] Another reconnaissance aircraft investigated the system several hours later and found supporting evidence for the NHC to upgrade the depression to Tropical Storm Arthur at 03:00 UTC on May 17.[20] Featuring the formation of a pre-season tropical storm, the 2020 Atlantic hurricane season became the sixth consecutive season with a tropical cyclone before the official June 1 start date.[21] The system managed to intensify slightly off the coast of Florida and Georgia. Even though the system was moving through the warmest waters of the Gulf Stream,[22] the satellite appearance began to degrade as it neared the coast of North Carolina, plagued by dry air and moderate wind shear.[23] However, Arthur reorganized early on May 18 and even strengthened slightly before making a close pass to the Outer Banks.[24] Later that day, the storm moved into an area of higher wind shear, exposing its center of circulation and marking the beginning of its extratropical transition,[25] a process Arthur completed by 15:00 UTC May 19, well east of southern Virginia.[26]

Passing within 20 nautical miles of the Outer Banks, the storm caused tropical storm force wind gusts and a single report of sustained tropical storm force winds at Alligator River Bridge.[25]

Tropical storm (SSHWS)
Duration	May 27 – May 28
Peak intensity	50 mph (85 km/h) (1-min)  1004 mbar (hPa)

On May 25, the NHC began to track thunderstorms associated with an elongated surface trough located over Florida and the adjoining Atlantic Ocean for potential development into a tropical cyclone, but did not expect formation due to strong upper-level winds.[27] However, contrary to predictions, the system organized after moving northwards, which in turn was contributed to an increase convection and winds within the system. Based on NWS Doppler radar data from Charleston and buoy data, the NHC initiated advisories on Tropical Storm Bertha at 12:00 UTC on May 27.[28] Bertha continued to strengthen despite its proximity to land.[29] One hour after the first advisory was issued, Bertha made landfall on the South Carolina coast with winds of 50 mph (80 km/h).[29] From formation until landfall, Bertha had an unusually small field of gale-force winds, stretching only 25 miles from the center.[30] Bertha began to weaken rapidly once inland, becoming a tropical depression just hours after landfall.[31] Bertha quickly degenerated to a post-tropical remnant over West Virginia at 9:00 UTC on May 28.[32] Bertha quickly enlarged as it became extratropical. Its remnants caused heavy rainfall and thunderstorms in the Great Lakes region before being absorbed by a larger extratropical system on May 29.

The precursor disturbance to Bertha caused a significant, multi-day rainfall event across South Florida, with accumulations of 8–10 in (200–250 mm) across several locations, and with a maximum 72-hour accumulation of 14.19 in (360 mm) in Miami.[33] The city observed a 24-hour total of 7.4 in (190 mm), more than doubling the previous daily rainfall record.[34] In and around Miami, the rains flooded homes and roadways, especially in close proximity to canals.[35] Some homes even reported partial roof collapses throughout Hallandale Beach and Hollywood as a result of the heavy precipitation.[36] Local police in El Portal asked that the South Florida Water Management District open floodgates to relieve flooding in those canals.[37] In Hialeah, several vehicles were stranded in flooded roadways, prompting several water rescues.[35] Days of heavy rainfall prompted local National Weather Service offices to issue flash flood warnings, and sporadic severe thunderstorms prompted additional advisories. An EF1 tornado caused primarily tree and fencing damage in southern Miami, though several campers were also overturned.[38] Gusts associated with the disturbance in Florida topped out at 51 mph (82 km/h) near Key Biscayne.[39] Even as the system progressed north away from Florida, the outer fringes of Bertha contributed to stormy weather across the state on May 27, forcing the postponement of the planned Crew Dragon Demo-2 launch.[40] In South Carolina, one death occurred by drowning due to rip currents.[41] One death, a drowning, related to rip currents in Myrtle Beach[42] and USD$200 million in damage were caused by Bertha.[43]

Tropical storm (SSHWS)
Duration	June 1 – June 10
Peak intensity	60 mph (95 km/h) (1-min)  992 mbar (hPa)

On May 31, the NHC started to note that Tropical Depression Two-E in the Eastern Pacific, later to be known as Tropical Storm Amanda, would have the potential to redevelop in the Bay of Campeche.[44] Amanda would then make landfall in Guatemala, its low-level circulation dissipating by 21:00 UTC that day. Its remnants moved north-northwest to the Bay of Campeche and began to re-develop over the Yucatan Peninsula.[45] At 21:00 UTC on June 1, the remnants of Amanda redeveloped into Tropical Depression Three over the Bay of Campeche. The depression very slowly moved west over the Bay of Campeche and intensified into a tropical storm at 15:15 UTC June 2, and it was named Cristobal.[46][47] This marked the earliest third named storm in the Atlantic, beating the previous record set by Tropical Storm Colin which became a tropical storm on June 5, 2016.[48] Throughout the remainder of the day, Cristobal's windfield became more symmetrical and well defined,[49] and it gradually strengthened with falling barometric pressure as the storm meandered towards the Mexican coastline.[50] Cristobal made landfall as a strong tropical storm just west of Ciudad del Carmen at 13:35 UTC on June 3 at its peak intensity of 60 mph (95 km/h).[51] Cristobal moved very slowly inland, and it weakened back down to tropical depression status as the overall structure of the storm deteriorated while it remained quasi-stationary over southeastern Mexico.[52]

The storm began accelerating northwards on June 5 as an arced band of convection began to develop over the northern and eastern sides of the storm.[53] By 18:00 UTC that day, despite being situated inland over the Yucatan peninsula, Cristobal had reintensified back to tropical storm status.[54] As Cristobal moved further north into the Gulf of Mexico, dry air and interaction with a upper-level trough to the east began to strip Cristobal of any central convection, with most of the convection being displaced east and north of the center.[55][56] Just after 22:00 UTC on June 7, Cristobal made landfall over southeastern Louisiana. Cristobal weakened to a tropical depression the next day as it moved inland over the state.[57] Cristobal, however, survived as a depression as it moved up the Mississippi River Valley until finally becoming extratropical at 3:00 UTC on June 10 over Iowa.[58]

On June 1, the government of Mexico issued a tropical storm warning from Campeche westward to Puerto de Veracruz.[59] Residents at risk were evacuated. 9,000 Mexican National Guard members were summoned to aid in preparations and repairs.[60] Significant rain fell across much of Southern Mexico and Central America. Wave heights up to 9.8 ft (3 m) high closed ports for several days. In El Salvador, a mudslide caused 7 people to go missing. Up to 9.6 in (243 mm) of rain fell in the Yucatan Peninsula, flooding sections of a highway. Street flooding occurred as far away as Nicaragua.[60] On June 5, while Cristobal was still a tropical depression, a tropical storm watch was issued from Punta Herrero to Rio Lagartos by the government of Mexico[61] as well as for another area from Intracoastal City, Louisiana to the Florida-Alabama border, issued by the National Weather Service.[62] These areas were later upgraded to warnings and for the Gulf Coast, the warning was extended to the Okaloosa/Walton County line.

Tropical storm (SSHWS)
Duration	June 22 – June 24
Peak intensity	45 mph (75 km/h) (1-min)  1002 mbar (hPa)

On June 19, the NHC began monitoring an area of disturbed weather off the Southeastern US coast for possible subtropical development in the short-term.[63] Slowly moving northwest, the system developed into a more defined non-tropical low pressure system by early on June 21.[64] However at the time, the low pressure system was not considered likely to develop due to unfavorable sea surface temperatures.[65] The system's circulation slowly grew more defined throughout the day and some thunderstorms began to develop near the circulation, but the system exited the warmer waters of the Gulf Stream later that same evening and began to lose any convection that developed.[66] Contrary to predictions, the low moved south back into the Gulf Stream in the afternoon of June 22 after struggling to develop convection, and new thunderstorm activity began to fire near the circulation.[67] The low's convective activity rapidly became more defined and well-organized while the circulation became closed, prompting the National Hurricane Center to upgrade the system into Subtropical Depression Four at around 21:00 UTC on June 22.[68] On June 23, the system's wind field had contracted significantly, becoming more characteristic of a tropical cyclone, while also strengthening further with winds to gale force, allowing the NHC to upgrade the system and designate it as Tropical Storm Dolly at approximately 16:15 UTC with winds of 45 mph (75 km/h).[69] This event marked the third earliest occurrence of the fourth named storm in the calendar year on record, behind only Tropical Storm Debby of 2012 and Tropical Storm Danielle of 2016.[3][70] Dolly was also the farthest north forming system on record before July 1 in the Atlantic, and the second farthest north forming named storm on record in the North Atlantic before August 1.[71] However, Dolly's peak intensity proved to be short lived as its central convection began to diminish while it drifted over colder ocean waters, and the storm consequently weakened.[72] At 15:00 UTC on June 24, Dolly became a post-tropical cyclone, with any remaining convection displaced well to the system's south and the remaining circulation exposed.[73]