NATIONAL HURRICANE CENTER TROPICAL CYCLONE REPORT TROPICAL STORM CRISTOBAL (AL032020) 1–9 June 2020 Robbie Berg National Hurricane Center 13 January 2021 PHOTO OF TROPICAL STORM CRISTOBAL TAKEN FROM THE INTERNATIONAL SPACE STATION ON JUNE 8, 2020 (IMAGE COURTESY OF NASA AND ASTRONAUT CHRIS CASSIDY [@ASTRO_SEAL]) Tropical Storm Cristobal, in conjunction with a larger weather system over Central America and Tropical Storm Amanda over the eastern Pacific Ocean, produced significant rainfall and flooding over portions of Central America and southeastern Mexico. Cristobal then went on to affect portions of the central U.S. Gulf coast with tropical-storm-force winds, significant storm surge, and heavy rainfall. Cristobal took the lives of six people in the United States and Mexico. Tropical Storm Cristobal 2 Tropical Storm Cristobal 1–9 JUNE 2020 SYNOPTIC HISTORY In late May, a Central American gyre1 developed and became centered near the Mexico/Guatemala border, while Tropical Storm Amanda concurrently formed over the far eastern North Pacific off the coasts of Guatemala and El Salvador. Amanda moved northeastward within the gyre and made landfall on the Pacific coast of Guatemala on 31 May, with its center dissipating over the mountainous terrain of that country late in the day. The remnant low pressure area continued to rotate northward and then northwestward across northern Guatemala and southeastern Mexico within the Central American gyre, emerging over the Bay of Campeche south of the city of Campeche, Mexico, around midday on 1 June. The low acquired a well- defined center and sufficiently organized deep convection soon after moving over water, marking the regeneration2 of a tropical depression at 1800 UTC 1 June about 35 n mi southwest of Campeche. The depression moved generally westward over the Bay of Campeche and strengthened to a tropical storm by 1200 UTC 2 June while centered about 65 n mi northwest of Ciudad del Carmen, Mexico. The “best track” chart of the tropical cyclone’s path is given in Fig. 1, with the wind and pressure histories shown in Figs. 2 and 3, respectively. The best track positions and intensities are listed in Table 13. Because Tropical Storm Cristobal was still embedded within the Central American gyre, it proceeded to make a slow counterclockwise loop over the Bay of Campeche and southeastern Mexico over the next several days, initially moving slowly southward and then southeastward on 2 and 3 June after becoming a tropical storm. Cristobal gradually strengthened during that period while over the warm waters of the Bay of Campeche, and it reached an estimated peak intensity of 50 kt by 0600 UTC 3 June. The storm maintained that intensity through landfall, which occurred around 1300 UTC near the town of Atasta, Mexico, just to the west of Ciudad del Carmen. Cristobal gradually weakened while it moved southeastward across the states of Campeche and Tabasco, and it became a tropical depression by 1200 UTC 4 June just before reaching the Guatemala border. The center continued on its counterclockwise track, moving eastward and then northeastward across far northern Guatemala and back over Mexico late on 4 June and early on 5 June. 1 A Central American gyre (CAG) is a broad lower-tropospheric cyclonic circulation occurring near Central America. For more information, please refer to Papin, P., L. F. Bosart, R. D. Torn, 2017: A Climatology of Central American Gyres. Mon. Wea. Rev., 145, 1983–2000. http://journals.ametsoc.org/doi/pdf/10.1175/MWR-D-16-0411.1 2 Protocol dictates that if the remnants of a former tropical cyclone regenerate in a new basin, the regenerated tropical cyclone is given a new designation. Since Amanda dissipated over Central America, the regenerated tropical cyclone was designated with the next name on the Atlantic list, Cristobal. (National Hurricane Operations Plan, Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM)). 3 A digital record of the complete best track, including wind radii, can be found on line at ftp://ftp.nhc.noaa.gov/atcf. Data for the current year’s storms are located in the btk directory, while previous years’ data are located in the archive directory. Tropical Storm Cristobal 3 On the morning of 5 June, winds increased to tropical storm force in the eastern part of Cristobal’s circulation along the eastern coast of the Yucatan Peninsula, and it is estimated that the system restrengthened to a tropical storm at 0600 UTC, even though its center was still over land about 80 n mi south-southeast of Campeche. Cristobal then turned northward, and its center remained over land for another 12 to 15 h before re-emerging over the southern Gulf of Mexico near Progreso, Mexico, late on 5 June. Cristobal’s maximum winds continued to increase in a convective band over the waters north of the Yucatan Peninsula even before the center re-emerged over the Gulf of Mexico, and the storm reached another estimated peak intensity of 50 kt at 0000 UTC 6 June while centered about 45 n mi north-northwest of Progreso. Cristobal’s maximum winds decreased slightly to 45 kt by 1200 UTC 6 June while the storm moved northward across the central Gulf of Mexico through a break in the subtropical ridge. Even though deep-layer shear over the Gulf of Mexico was relatively low and sea surface temperatures were between 27°C and 28°C, Cristobal’s broad structure, and possibly some dry air in the middle levels of the atmosphere, did not favor re-intensification. Consequently, the cyclone’s intensity held steady at 45 kt until landfall in Plaquemines Parish, Louisiana, just east of Grand Isle, around 2200 UTC 7 June. A blocking high caused Cristobal to slow down and turn northwestward while its center moved across the New Orleans metropolitan area, and the cyclone weakened to a tropical depression by 1200 UTC 8 June when it was centered near the Louisiana/Mississippi border about 10 n mi west-northwest of Natchez, Mississippi. An advancing deep-layer trough over the Rocky Mountains pushed the blocking high eastward, and Cristobal subsequently moved northward and north-northeastward across Arkansas, Missouri, and southeastern Iowa on 8 and 9 June. Cristobal was absorbed within the trough and became an extratropical low by 0000 UTC 10 June while centered about 15 n mi north- northwest of Dubuque, Iowa, just before crossing the border into Wisconsin. During 10 June, the extratropical low turned northeastward across Wisconsin, the Upper Peninsula of Michigan, and eventually Ontario, Canada, producing gale-force winds across portions of Lake Superior and Lake Michigan. The low then slowed down and meandered when it reached southern Hudson Bay on 11 June, and it dissipated soon after 0600 UTC 12 June about 30 n mi south-southwest of Wemindji, Quebec. METEOROLOGICAL STATISTICS Observations in Cristobal (Figs. 2 and 3) include subjective satellite-based Dvorak technique intensity estimates from the Tropical Analysis and Forecast Branch (TAFB), and objective Advanced Dvorak Technique (ADT) estimates and Satellite Consensus (SATCON) estimates from the Cooperative Institute for Meteorological Satellite Studies/University of Wisconsin-Madison. Observations also include flight-level, stepped frequency microwave radiometer (SFMR), and dropwindsonde observations from seven flights of the 53rd Weather Reconnaissance Squadron of the U.S. Air Force Reserve Command and two flights of the NOAA Aircraft Operations Center (AOC) WP-3D aircraft. Data and imagery from NOAA polar-orbiting satellites including the Advanced Microwave Sounding Unit (AMSU), the NASA Global Precipitation Mission (GPM), the European Space Agency’s Advanced Scatterometer (ASCAT), Tropical Storm Cristobal 4 and Defense Meteorological Satellite Program (DMSP) satellites, among others, were also useful in constructing the best track of Cristobal. Ship reports of winds of tropical storm force associated with Cristobal are given in Table 2, and selected surface observations from land stations and data buoys are given in Table 3. Rainfall totals from southeastern Mexico and Central America are provided in Table 4. Winds and Pressure Cristobal’s first estimated peak intensity of 50 kt from 0600 UTC until landfall at 1300 UTC 3 June along the coast of Mexico is based on a blend of a peak 850-mb flight-level wind of 55 kt (which adjusts to about 45 kt at the surface) and SFMR-measured winds of 52 kt. Height-adjusted winds of 45 to 50 kt were measured at a couple of Mexican oil rigs early on 3 June and also support Cristobal’s estimated peak intensity of 50 kt. Surface observations and scatterometer data indicate that Cristobal regained tropical storm status while its center was still over southeastern Mexico, with tropical-storm-force winds occurring along the eastern coast of the Yucatan Peninsula on the morning of 5 June. A Weatherflow station at Cancun measured a sustained wind of 40 kt at 1451 UTC, while an ASCAT pass around the same time showed surface winds as high as 38 kt. Cristobal’s second estimated peak intensity of 50 kt north of the Yucatan Peninsula is based on a peak 850-mb flight-level wind of 68 kt (which adjusts to about 54 kt at the surface) and an SFMR wind of 52 kt, which were measured in a convective band by an Air Force Reserve aircraft as it began heading back to base at the end of its mission early on 6 June. These data allow for the possibility that the peak intensity was even a little higher than 50 kt, but the aircraft’s sampling within the convective environment well away from the center of circulation argues that higher measurements may not be as representative of the cyclone’s intensity. Cristobal’s estimated intensity of 45 kt at its landfall on the Louisiana coast at 2200 UTC 7 June is based on aircraft reconnaissance data from earlier that morning, surface observations from southeastern Louisiana and southern Mississippi, and NWS Doppler radar velocity data.