Hurricane Franklin, the first Atlantic Basin Hurricane in the GOES-R era, approached the east coast of Mexico during the evening of 09 August 2017. One strategy to observe a smooth day/night transition, discussed in a previous blog post, involves combining visible and infrared imagery. For this case, we take it a step further by including the sandwich VIS/IR combo during the day, and transition to just IR at night. The sandwich combo, also discussed in previous posts, has a VIS underlay with a semi-transparent IR overlay of only the coldest cloud tops. GOES-16 was undergoing testing on the 9th, so no 1-min meso sectors were available, leaving “only” 5-min imagery to observe Franklin.

Figure 1: 08 August 2017 VIS/IR Sandwich combo during day transition to IR at night for Hurricane Franklin. Full resolution: https://satelliteliaisonblog.files.wordpress.com/2017/08/20170809_hurr_transition_sw2_anno.gif

-Bill Line, NWS

“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.”

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.

NHC 3-day Forecast Track,Initial Wind Field and Watch/Warning Graphic for Tropical Storm Franklin on 06 August 2017, 11 PM EDT – the first advisory after being classified a Tropical Storm. (http://www.nhc.noaa.gov/archive/2017/FRANKLIN.shtml?)

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:

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.

ASCAT-A pass mentioned in the above TCD.  Source:  https://manati.star.nesdis.noaa.gov/datasets/ASCATData.php/ASCATData.php

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.

Full-disk GOES-16 Nighttime Microphysics RGB imagery over the pre-Franklin disturbance from 0-6 UTC on 8/7/17.  **THIS DATA IS PRELIMINARY AND NOT OPERATIONAL**

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.

CONUS GOES-16 Nighttime Microphysics RGB imagery over the pre-Franklin disturbance from 0-6 UTC on 8/7/17.  **THIS DATA IS PRELIMINARY AND NOT OPERATIONAL**

-Andrea Schumacher, CIRA/CSU and Michael Folmer, CICS/UMD

“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.”