The Geostationary Lightning Mapper (GLM) instrument, onboard NOAA’s GOES-19 satellite, is now continuously observing lightning over the Western Hemisphere. GOES-19 launched on June 25, 2024. GLM detects and maps total lightning—in-cloud, cloud-to-cloud, and cloud-to-ground—continuously over the Americas and adjacent ocean regions. GLM offers insights beyond the presence of a lightning strike, revealing the spatial and temporal extent of lightning flashes.
Recently, the GOES-19 GLM detected and monitored lightning activity in two extremely hazardous hurricanes. On Sept. 24, 2024, GLM observed widespread lightning as a cluster of thunderstorms in the western Caribbean Sea consolidated into Tropical Storm Helene. Continuous lightning in the outer rain bands was accompanied by occasional eyewall lightning, as Hurricane Helene rapidly intensified in the eastern Gulf of Mexico.
Frequent lightning completely enveloped the eyewall as the storm intensified further on its final approach to the Florida coastline. Away from the storm center, GLM helped identify the most intense thunderstorms most likely to produce tornadoes.
Such widespread weather events pose particular challenges for the aviation industry. Increased lightning flashes, as recently observed by GLM, occur in storms with more turbulent updrafts and downdrafts, which are a significant hazard to aircraft. GLM imagery helps pilots and air traffic controllers route flights to maximize safety and minimize economic impacts, including areas over oceans without radar coverage.
Observations are also critical for analyzing tropical cyclone location, intensity, and size, and for forecasting these parameters. GLM provides a unique dataset that aids tropical cyclone analysis and forecasting. The lightning detected by GLM provides insight into the vigor and pattern of convection below the cloud tops in tropical cyclones, and unlike microwave imagery, is able to do so continuously from geostationary orbit.
Only two weeks after Helene formed, GLM again observed widespread thunderstorms as they consolidated into Hurricane Milton. Persistent deep convection over the northwestern portion of the circulation along with some increase in rain bands led forecasters to begin initiating advisories on this storm.
Continuous eyewall lightning revealed the establishment of a robust inner core as Milton rapidly intensified. Continuous eyewall lightning persisted as the storm grew in size and strength in the southern Gulf of Mexico. Frequent lightning outside the storm core was associated with intense rain bands that produced widespread flash flooding and tornadoes across Florida on Oct. 9, 2024. Milton made landfall near Siesta Key, Florida, as a Category 3 hurricane later that evening.
In the six years since the first GLM data became available from GOES-16, GLM observations have become a staple of forecaster monitoring of storms, capitalizing on scientific advances. Rapidly updating GLM data gives forecasters the ability to monitor lightning flashes with pinpoint precision over much of the Western Hemisphere.
GOES-19 is currently undergoing post-launch testing, validation and calibration of its instruments and systems to prepare it for operations. NOAA plans for GOES-19 to replace GOES-16 as GOES East in April 2025.
Imagery and data from GOES-19 during the post-launch testing phase should be considered preliminary and non-operational.