The GOES-16 7.3 and 10.4 micrometer bands show the evolution of two extreme rainfall events in northern Peru and southern Ecuador during the evenings of March 21 and March 23, 2017. Rainfall in this region of the world comes in the form of downpours from evening thunderstorms. The warming of sea surface temperatures to readings over 29°C largely enhances these storms. When these temperatures are present, and under favorable synoptic setups, storms grow into large storm clusters that are capable of producing 4-8 in of rain in a few hours. The heaviest rains often develop in areas where the southern band of the Intertropical Convergence Zone (ITCZ) enters the coast.
The thunderstorms exhibit a marked diurnal cycle. Convection develops during the late afternoon in the western slopes of the Andes and interior of the coast. While propagating westward into the evening, ongoing convective cells interact with diurnal breezes and unstable air masses that brew over the coast during the morning and afternoon. The additional moisture convergence and instability boosts the thunderstorms leading to heavy evening rains. The storms tend to rain the heaviest during the evening and near midnight, to then migrate west into the Pacific Ocean while losing organization. The storms of the evening of March 21st produced over 12 hours of rainfall in some locations. Several stations reported totals over 4 inches, and major flooding occurred in the cities of Piura, Paita and Talara, among others.
GOES-16 data will be of great use to improve the weather forecasts in Peru. The improved spatial and temporal resolution, plus the additional spectral bands, provide much more information that will serve to better understand and monitor the complex processes involved in these heavy rainfall events. Better monitoring implies better forecasts. GOES-16 data will allow forecasters to fine-tune the location of the potentially heaviest rains, better estimate storm propagation, and estimate regions of intensification and weakening.
As an example, data from the 7.3 μm channel can be used to monitor the locations where the largest low-mid tropospheric water vapor content is present. This helps to narrow down the location of the ITCZ, and provides information about the amount of moisture that may be available for rain. By contrasting the structure and movement of cirrus versus low-mid tropospheric background water vapor, the 7.3 μm channel provides information about atmospheric motion at different levels, and potential areas of enhanced upper divergence.
The 10.3 μm band provides more insight about what is occurring in the lower troposphere. This band is particularly useful to find surface features such as mesoscale convergence bands that form within the ITCZ, which produce a localized enhancement of rains; and to evaluate low-level winds. In this region of the world, weak surface winds or westerlies are favorable for strong evening convection, as they enhance diurnal onshore breezes. The 10.3 μm channel also provides more detail about the evolution of shallow convection. It provides insight about regions where convection might develop, and also suggests where low-level inversions may be present, from horizontally expanding warm clouds and waves propagating in these environments.
Thanks for reading!
Jose Galvez (WPC), Michael Folmer (CICS), and Michel Davison (WPC)
“The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. Users bear all responsibility for inspecting the data prior to use and for the manner in which the data are utilized.”