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|Tropical storm (SSHWS/NWS)|
|Formed||June 14, 2018|
|Dissipated||June 19, 2018|
|Highest winds||1-minute sustained: 65 mph (100 km/h) |
|Lowest pressure||997 mbar (hPa); 29.44 inHg|
|Areas affected||Central and Southern Mexico|
|Part of the 2018 Pacific hurricane season|
Tropical Storm Carlotta was a tropical cyclone that caused flooding within several states in southwestern and central Mexico. Carlotta formed as the result of a breakdown in the Intertropical Convergence Zone to the south of Mexico. On June 12, a broad area of low pressure formed several hundred miles south of the aforementioned country and strengthened into a tropical storm by June 15. On the next day, the storm unexpectedly stalled within a favorable environment, which led to more intensification than originally anticipated. Early on June 17, Carlotta reached peak intensity with maximum sustained winds of 65 mph (100 km/h) and a minimum central pressure of 997 mbar (29.44 inHg) while located only 30 mi (50 km) south-southeast of Acapulco. Soon after, Carlotta began to interact with land and experience wind shear, which resulted in the system weakening to tropical depression status later in the day. The storm weakened to a remnant low early on June 19 and dissipated several hours later.
Carlotta prompted the issuance of multiple watches and warnings for the southern coast of Mexico. The storm caused a total of three deaths; two in Aguascalientes and one in Oaxaca. Additionally, the storm caused flooding and landslides throughout the states of Aguascalientes, Guerrero, Michoacán, Oaxaca, and Puebla, as well as the Yucatán Peninsula. Damage from the system was reported to be minor.
Tropical Storm Carlotta formed as the result of a breakdown in the Intertropical Convergence Zone to the south of Mexico. However, a tropical wave that crossed over Central America around June 11 may have contributed to Carlotta's formation as well. On June 12, the National Hurricane Center (NHC) reported that a broad area of low pressure had formed several hundred miles south of southeastern Mexico. The NHC continued to monitor the disturbance over the next couple days as it drifted northward. Initially, strong upper-level winds prevented development, but the system unexpectedly organized on June 14. Following structural improvements, the NHC upgraded the system into a tropical depression at 18:00 UTC while about 140 mi (220 km) south of Acapulco. Around that time, the NHC forecast that a mid-level ridge over Mexico would weaken on the next day, leaving the depression in an area of light steering currents. Despite being located in an environment with low to moderate wind shear and sea surface temperatures exceeding 86 °F (30 °C), the depression experienced minimal change in intensity over the next 18 hours. After the system's center reformed farther north, the NHC reduced its intensity forecast as the storm would have less time over water. However, Carlotta never made landfall during its existence as a tropical cyclone. Around 18:00 UTC on June 15, the system strengthened into a tropical storm, after which it was assigned the name Carlotta. The system's intensity then leveled off for about twelve hours.
Early on June 16, Carlotta's forward motion began to fluctuate, changing from northeast to southeast in six hours. Carlotta began to intensify again around 06:00 UTC as it stalled off the coast of Mexico. Soon after, the cyclone began moving in a northerly direction. Over the next twelve hours, Carlotta experienced little change in organization before peaking at 00:00 UTC on June 17 with maximum sustained winds of 65 mph (100 km/h) and a minimum central pressure of 997 mbar (29.44 inHg) while located only 30 mi (50 km) south-southeast of Acapulco. Around that time, the NHC noted that the system's structure had improved significantly, with a contracting eye and more symmetric eyewall. Soon after, Carlotta began to weaken due to increasing interactions with land and northerly wind shear. Meanwhile, the system had begun tracking towards the northwest. Around 18:00 UTC on the same day, Carlotta weakened into a tropical depression after lacking organized deep convection for several hours. Over the next day, Carlotta continued to weaken before degenerating into a remnant low on June 19 at 00:00 UTC. Soon after, Carotta's upper-level circulation decoupled entirely and drifted towards the southwest, while the low- and mid-level remnants remained. Carlotta's remnants dissipated around 06:00 UTC while located offshore of the coast between Manzanillo and Zihuatanejo, Mexico.
On June 14 at 21:00 UTC, the government of Mexico issued a tropical storm watch for Tecpan de Galeana to Punta Maldonado . Six hours later, the watch was upgraded to a tropical storm warning. On June 15 at 15:00 UTC, the tropical storm warning was extended to Lagunas de Chacahua. Six hours later, the warning was discontinued for Tecpan de Galeana to west of Acapulco. On June 17 at 03:00 UTC, the warning was extended westward from Acapulco to Tecpan de Galeana and cancelled to the east of Punta Maldonado. At 09:00 UTC, the warning was discontinued east of Tecpan de Galeana and extended westward to Lazaro Cardenas. The tropical storm warning was cancelled at 18:00 UTC, after Carlotta weakened into a tropical depression.
Tropical Storm Carlotta caused flooding in southern Mexico, with the states of Aguascalientes, Guerrero, Michoacán, Oaxaca, Puebla, and the Yucatán Peninsula being affected. Additionally, Carlotta caused two deaths in Aguascalientes and one in Oaxaca. In the Yucatán Peninsula, Carlotta, a tropical wave, and another low-pressure system dropped between 70–400 mm (3–20 in) of rain, causing severe flooding. In Tizimín, the Popolnáh police station was inundated and the DN-III-E Plan, a plan for the coordination of search and rescue operations and disaster aid, was activated to help with recovery efforts.
In Oaxaca, severe flooding killed one individual. Fishermen recovered the body of a 29-year-old man about 10 mi (20 km) off the coast after he was dragged away by flood waters and drowned. The proximity of Carlotta prompted the closure of the ports of Huatulco, Puerto Ángel, and Puerto Escondido and the suspension of fishing operations. Additionally, multiple landslides occurred in the state. In Guerrero, only minor damage occurred. In the Costa Chica region, the storm damaged several palapas on a beach and the fishing equipment of at least 80 families, preventing them from working. In the municipalities of Tecpan de Galeana, Zihuatanejo, and Petatlán, 42 homes were inundated by flood waters. A total of 138 trees were downed in Acapulco and several other municipalities. In Acapulco, a hospital sustained damage to its windows and four injuries were reported. Additionally, 32 neighborhoods lost power, nine houses lost their roofs, and 11 roads collapsed. In Tehuacán, Puebla, homes and businesses flooded, multiple cars were stranded, and several trees fell. Additionally, a state highway and a bridge collapsed, cutting off several towns in the area. 
In Michoacán, multiple cities along the coast experienced severe flooding. In Melchor Ocampo, a peak rainfall total of 285.0 mm (11.2 in) occurred. Approximately 210.6 mm (8.291 in) of rain fell in La Villita while 194.9 mm (7.673 in) was recorded in Presa La Villita. Rainfall caused the Acalpican River to overflow its banks. In the Tiquicheo Municipality, 10 houses flooded after a river near the city overflowed its banks. Additionally, multiple homes were inundated in the Zamora Municipality. In Pátzcuaro, multiple landslides occurred, damaging roads in the region. In Nuevo Urecho, the overflow of the Los Hervores River damaged water pumps, resulting in a water shortage throughout the municipality. Throughout the storm, 35 temporary shelters were in operation in Michoacán.
In Aguascalientes, Carlotta caused infrastructural damage and two indirect deaths in Aguascalientes City. Rainfall from Carlotta flooded streets, sweeping away dozens of cars and prompting the rescue of several people. Two women became entrapped in their vehicle due to rising flood waters and died of carbon monoxide poisoning. After 57 mm (2.2 in) of rain fell, the city's drainage system collapsed. Moreover, 12 trees fell and 12 houses were flooded. Additionally, a waterspout touched down in the state. Mexican authorities alerted the public that the El Cedazo dam had the potential to overflow due to the heavy rainfall, although no overflow actually occurred.
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