The National Hurricane Center (NHC) first noted the potential of the formation of a tropical cyclone in the Gulf of Mexico during the mid-afternoon hours of June 12.
At the time, an upper-level trough was producing disorganized showers and thunderstorms over the northwestern Caribbean Sea, Belize, and the Yucatán Peninsula.
However, the NHC assessed a low probability as atmospheric conditions were assessed to be unfavorable in the Gulf of Mexico.
Moving northwestward, the system tracked over the Yucatán Peninsula, and development chances increased as forecasts showed a more favorable environment within the Gulf of Mexico.
Early on June 14, the trough began to interact with an upper-level low over the Gulf of Mexico, producing additional showers over portions of Central America.
Later that day, Hurricane Hunters aircraft reconnaissance began investigating the system, and discovered an ill-defined but intact and broad low-pressure area over the south-central Gulf of Mexico.
The system continued to possess an elongated circulation through June 15, but on June 16, reconnaissance aircraft indicated that the storm had become sufficiently organized to be considered a tropical cyclone.
As winds were already found to have met the threshold for a tropical storm, the NHC began issuing advisories on Tropical Storm Bill at 03:00 UTC that day, skipping the tropical depression classification.

Moving towards the west-northwest and already near the United States Gulf Coast, the NHC's official forecast at the time of Bill's formation indicated that the storm would not have much time to strengthen over water.
However, meteorologists Jeff Masters and Bob Henson of Weather Underground noted the possibility of Bill strengthening over land via the brown ocean effect due to floods in the previous month that helped saturate soils in Texas and Oklahoma.
The cyclone's organization remained steady as the storm approached the coast, with most of the convection taking place around the storm's eastern half, with rainbands primarily occupying the eastern and southern portions of Bill's circulation.
At 15:00 UTC on June 16, Bill reached its peak intensity with maximum sustained winds of 60 mph (95 km/h) and a minimum barometric pressure of 997 mbar (hPa; 29.44 inHg) as the storm was located 15 mi (20 km) south of Port O'Connor, Texas.
At peak intensity, Bill made landfall on Matagorda Island at 16:45 UTC and began moving into inland Texas.
At 09:00 UTC on June 17, Bill was downgraded to tropical depression intensity, though it maintained an organized structure.
The next day, Bill had rapidly deteriorated as it moved northeastward.
However, the system's strength slowly weakened.
Operationally, it was announced that Bill stayed tropical throughout most of its lifetime, being declared a remnant low on June 20 by the WPC, however the NHC's post storm analysis revealed that Bill had degraded into a remnant low on June 18, while the storm was situated over Tulsa, Oklahoma.
Bill's remnant low continued to move eastward for several more days, before being absorbed by another extratropical system on June 23.
The National Hurricane Center (NHC) first noted the potential of the formation of a tropical cyclone in the Gulf of Mexico during the mid-afternoon hours of June 12. At the time, an upper-level trough was producing disorganized showers and thunderstorms over the northwestern Caribbean Sea, Belize, and the Yucatán Peninsula. However, the NHC assessed a low probability as atmospheric conditions were assessed to be unfavorable in the Gulf of Mexico. Moving northwestward, the system tracked over the Yucatán Peninsula, and development chances increased as forecasts showed a more favorable environment within the Gulf of Mexico. Early on June 14, the trough began to interact with an upper-level low over the Gulf of Mexico, producing additional showers over portions of Central America. Later that day, Hurricane Hunters aircraft reconnaissance began investigating the system, and discovered an ill-defined but intact and broad low-pressure area over the south-central Gulf of Mexico. The system continued to possess an elongated circulation through June 15, but on June 16, reconnaissance aircraft indicated that the storm had become sufficiently organized to be considered a tropical cyclone. As winds were already found to have met the threshold for a tropical storm, the NHC began issuing advisories on Tropical Storm Bill at 03:00 UTC that day, skipping the tropical depression classification.
Moving towards the west-northwest and already near the United States Gulf Coast, the NHC's official forecast at the time of Bill's formation indicated that the storm would not have much time to strengthen over water. However, meteorologists Jeff Masters and Bob Henson of Weather Underground noted the possibility of Bill strengthening over land via the brown ocean effect due to floods in the previous month that helped saturate soils in Texas and Oklahoma. The cyclone's organization remained steady as the storm approached the coast, with most of the convection taking place around the storm's eastern half, with rainbands primarily occupying the eastern and southern portions of Bill's circulation. At 15:00 UTC on June 16, Bill reached its peak intensity with maximum sustained winds of 60 mph (95 km/h) and a minimum barometric pressure of 997 mbar (hPa; 29.44 inHg) as the storm was located 15 mi (20 km) south of Port O'Connor, Texas. At peak intensity, Bill made landfall on Matagorda Island at 16:45 UTC and began moving into inland Texas. At 09:00 UTC on June 17, Bill was downgraded to tropical depression intensity, though it maintained an organized structure. The next day, Bill had rapidly deteriorated as it moved northeastward. However, the system's strength slowly weakened. Operationally, it was announced that Bill stayed tropical throughout most of its lifetime, being declared a remnant low on June 20 by the WPC, however the NHC's post storm analysis revealed that Bill had degraded into a remnant low on June 18, while the storm was situated over Tulsa, Oklahoma. Bill's remnant low continued to move eastward for several more days, before being absorbed by another extratropical system on June 23.
Tropical Storm Bill (2015)