Over the weekend Tropical Storm (TS) Franklin formed off of the coast of Honduras, a prime location for viewing with GOES-16. NHC forecasters have found the higher spatial and temporal visible imagery very useful for analyzing genesis in the past. However, TS Franklin formed overnight, a time when visible satellite imagery is not available.
Fortunately, there are several new capabilities available from GOES-16 for nighttime viewing – including the Nighttime Microphysics (Advanced) RGB product (originally created by EUMETSAT). The Nighttime Microphysics RGB product uses infrared channels to provide information about the fundamental properties of clouds including drop size and phase (water, mixed phase, ice) at nighttime. It can help distinguish between ice phase clouds at high elevations and water phase clouds at lower elevations, providing a pseudo three-dimensional view of the atmosphere. NHC forecasters found this product particularly useful in determining whether or not TS Franklin had a closed surface circulation, a necessary condition for formation.
From the 5am Tropical Cyclone Discussion, it’s clear that the GOES-16 Nighttime Microphysics imagery provided forecasters with information that other data sources could not:
|WTNT42 KNHC 070849
Tropical Storm Franklin Discussion Number 3
NWS National Hurricane Center Miami FL AL072017
500 AM EDT Mon Aug 07 2017
Deep convection associated with Franklin has been steadily
increasing in both coverage and vertical depth since the previous
advisory. Wind data from a late-arriving 0231Z ASCAT-A pass suggest
that Franklin might not have had a closed surface circulation at
that time. However, the new GOES-16 nighttime microphysics imagery
clearly shows low clouds moving from west to east on the south side
of the alleged center, which is suggestive of a closed low-level
In the ASCAT image below, there are no westerly winds along the south side of the pre-Franklin disturbance (which was situated just off the coast of Honduras at this time), which would suggest the surface circulation was not yet closed.
However, in the GOES-16 Nighttime Microphysics imagery, the motion of small, low-level clouds along the south side of the pre-Franklin disturbance could be seen to have a westerly component of motion, indicating that the circulation may in fact be closed after all.
These low-level cloud motions were much easier to see in the 5-minute resolution imagery, which was available because the pre-Franklin disturbance was within the CONUS domain at this time.
-Andrea Schumacher, CIRA/CSU and Michael Folmer, CICS/UMD
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