Hurricane Ida made landfall along the Louisiana coast on 29 August 2021 as a category 4 Hurricane packing sustained wind speeds of 150 mph. Numerous wind gusts over 60 mph were measured at the surface onshore, including a few measured gusts over 100 mph. There were numerous reports of flash flooding, with a large swath of 6+” rainfall falling in the <24-hr period (Fig 1). There was also significant storm surge along the coast. This post will share select NOAA satellite imagery capturing Hurricane Ida. All imagery was created in AWIPS (unless otherwise noted).

GOES-East mesoscale sector (1-min) imagery was available for Ida throughout its evolution. The center of circulation (eye) cleared out quickly during a 2.5-hour period on the 28th, shown here in 1-min VIS (Fig 2). The health of the eye and surrounding thunderstorm activity can be studied in detail with the 1-min, 500 m resolution imagery.

At sunrise on the 29th, GOES-East 1-min VIS revealed the mature eye of the now major hurricane as it approached the Louisiana coast. Smaller scale circulations (mesovorticies) can be diagnosed in the 1-min VIS within the eye of the hurricane from sunrise on the 29th through landfall (Fig 3). The sun angle at sunrise allows the opportunity to investigate eyewall thunderstorm activity in better detail given the shadowing, as well as abundant gravity wave activity atop the clouds emanating away from the eye.

During a similar time period, a zoomed out view of GOES-East Natural Color Imagery characterizes the size of the storm with respect to the 1000 km x 1000 km mesoscale sector. GOES-East GLM Flash Points are overlaid (Fig 4).

A longer, 2-min resolution animation of visible imagery captures the period of Ida evolution from sunrise around 1217 UTC to to landfall at 1655 UTC (Fig 5).

GOES-East 2-min VIS+IR sandwich imagery combines the high detail of the VIS with the qualitative (brightness temperature) information of the IR into a single image during the period following landfall (Fig 6).

The full daytime evolution of the Ida is shown in 5-min CONUS VIS imagery in the following feature relative animation (Fig 7). The eye of the storm maintains itself well inland, possibly due in part to the marshlands along/near the coast.

An animation of VIS during the day and IR during the night with GLM flash points presents the evolution of Tornado (red), Severe Thunderstorm (yellow), Extreme Wind (magenta), Marine (cyan) and Flash Flood (green) Warnings with respect to the path of the hurricane and lightning progression (Fig 8).

The full evolution of Ida from just prior to becoming a hurricane to just after being downgraded to a tropical storm is shown in 30-min Geocolor+GLM Imagery (Fig 9) and VIS+IR sandwich daytime imagery transitioning to IR at night (Fig 10).

S-NPP and NOAA-20 VIIRS instruments also captured detailed views of Ida. The Day Night Band Near Constant Contrast product provided a detailed (750 m) “visible” imagery at night (Fig 11; expand Aug 28, 29, 30).

A VIIRS pass shortly after landfall on the 30th depicted the detailed IR structure of the storm (Fig 12).

Hurricane Ida made landfall in Louisiana on the 16-year university of Hurricane Katrina. A comparison between GOES-12 imagery of Katrina and GOES-16 imagery of Ida can be found on the STAR website, courtesy of Matthew Jochum, STAR.

GOES-17 (GOES-West) full disk imagery also captured Hurricane Ida with 10-min resolution (Fig 13 and 14). The high viewing angle provides an alternative perspective of the storm compared to that from GOES-East and VIIRS, specifically additional texture detail within the eye and surrounding convection. Full resolution GOES-17 iamgery created in McIDAS.

Ida Remnants continued north across the eastern United States through the early week. On 01 Sep, the storm brought an abundance of moisture to the northeast, resulting in heavy rain and widespread flash flooding, in addition to severe thunderstorms and tornados. A long animation of GOES-East IR and GLM flash points with NWS warning polygons overlaid captures the evolution of the storm through the northeast on the 1st and associated NWS warnings (Fig 15).

Focusing on the New York City area, GOES-East IR imagery reveals Ida associated thunderstorms that resulted in considerable flash flooding. Persistent cold and cooling cloud tops (< -70C) and overshooting tops can be diagnosed in the imagery over the region during the 4-hour period.

GOES-East hourly upper-level water vapor imagery shows the evolution of Ida from landfall on the 29th through exit of the northeast US on the 2nd (Figure 17). The imagery shows the increase in deep moisture across the eastern US during the period, and interaction of Ida with a shortwave trough and increasing mid-upper-level flow as the storm progressed north. Dry/descending air is diagnosed expanding across the eastern US in the wake of Ida.

ill Line, NESDIS and CIRA

There have been numerous large wildfires across the western US in recent years. After the fire reaches 100% containment, the danger is not over. The wildfire completely changes the hydrology of the landscape due to loss of groundcover and altered soil chemistry resulting in hydrophobicity (Fig 1). Therefore, flash flooding and debris flow are major concerns to life and property over, around, and downstream of burn scars in the years following a wildfire. The characteristics of the burn scar are monitored closely, and rainfall thresholds for the possible occurrence of flash flooding are established and modified over time. Given the considerable threat, forecasters in NWS offices must monitor shower and thunderstorm development closely around burn scars. Not only are they issuing Flash Flood products, but they are in constant contact with core partners regarding the latest developments with regard to the flash flood threat.

Satellite imagery is a vital tool utilized by forecasters when monitoring convective development near burn scars. Considering many of the western fires occur in remote, high-terrain regions, radar coverage is often degraded or not available at all to forecasters (beam blockage, distance from radar), making satellite data even more important to forecasters during such burn scar flash flooding situations. One-minute imagery has particular value in these rapidly evolving situations, allowing forecasters to diagnose boundary interactions and convective trends as early as possible. The example in Figure 2 is from a 2018 Hayden Pass burn scar flash flood event in which 1-min GOES-East VIS was leveraged for tracking convective growth, minute-by-minute, under high level cloud debris near a burn scar in a radar poor region. Forecasters are strongly encouraged to request a mesoscale sector when showers and thunderstorms are forecast in the vicinity of burn scars.

Prior to the development of the first cloud, forecasters monitor water vapor imagery for deep moisture availability and for subtle shortwave troughs that may force downstream convective initiation. Using a 30 July 2021 BOU burn scar flash flood event as an example (East Troublesome and Cameron Peak burn areas), subtle shortwaves could be diagnosed pushing north along the western periphery of a broad central US Ridge and within a stream of enhanced southerly moisture feed (Fig 3). The shortwaves advanced north across CO and eventually into the N CO Rockies, aiding in afternoon/evening convective initiation along the far eastern portion of the moisture stream and within weak mid-upper level flow.

Satellite products, specifically the Day Cloud Phase Distinction (DCPD) RGB, have particular value in the pre-convective environment, when forecasters are using it to monitor cumulus cloud growth and signs for convective initiation. The DCPD RGB captures initial cumulus cloud development (aqua colors), their initial vertical growth and eventual glaciation (aqua > green), and finally convective initiation and rapid vertical growth (green > yellow). By observing the early signs of near-future convective initiation near a burn scar (prior to any radar echoes), forecasters can provide very early alerts to their core partners detailing their latest thoughts on flash flooding risks over the burn scars. Figure 4 from the BOU example shows DCPD RGB evolution prior to the first Flash Flood Warnings. Cu are observed developing along the high terrain through the morning including over the burn scars, with several areas of glaciation developing by 1731 UTC over/near the burn scars. This would be a decision point for forecasters to alert partners of the growing convective threat near the burn scars.

Playing the animation through the afternoon, areas of the cu field continued to glaciate, with heavier rain showers and thunderstorms eventually developing over the burn scars resulting in the issuance of Flash Flood Warnings (Fig 5).

Another DCPD RGB example comes from the Grizzly Creek Burn scar on 03 July 2021. Forecasters monitoring trends in the 1-min RGB imagery across the area acknowledged the increasing potential for near-future development just upstream of the burn scar by 1951 UTC (Fig 6). Initiation had occurred west and east of the burn scar, while more immature cu were beginning to develop just to the northwest (upstream) of the burn scar in an area of untapped instability. Based on the favorable environment, likely storm motion, and trends in satellite imagery, a Flash Flood Watch was issued for the burn area at 2004 UTC.

Glaciation would occur shortly thereafter, followed by the development of thunderstorms and their advancement over the burn scar, per the 1-min DCPD RGB imagery. A Flash Flood Warning was issued for the burn scar at 2104 UTC, primarily based on the development of a lofted thunderstorm core diagnosed in radar imagery. The end result was numerous debris flows over interstate 70 around 2130 UTC.

Similarly and as convection continues to grow, VIS+IR Sandwich imagery is utilized by forecasters to monitor for growing convective threats to burn scars. The imagery maintains the high detail from the VIS, which is important for diagnosing cumulus cloud and storm top trends and details. At the same time, the imagery incorporates quantitative information (IR Brightness temperatures) for forecasters to further assess trends in convective development and heavy rain rate potential. Cooling convective tops represent strengthening thunderstorms, while, just as important, warming tops (and losing texture) signal a weakening trend. The example in Figure 8 occurs during the same time period as that in Figure 5. Areas of rapid cooling and coldest convective cloud tops are easily found in the sandwich imagery, and correlate to greatest heavy rain potential (and FFWs when over burn scars).

Another important use of these GOES imagery products, particularly far from the satellite subpoint, is to track the movement of the thunderstorm updraft. Oftentimes, these summertime thunderstorms over the high terrain develop in areas of weak steering flow, with anvil motion deviating considerably from actual storm movement. Therefore, it is important for forecasters to analyze the movement of the updraft in satellite imagery if possible, as slow moving storms anchored to the terrain pose an elevated flash flood threat. Finally, one must account for parallax when considering the location of thunderstorms with respect to the burn scar.

Bill Line (NESDIS and CIRA)

Input from Klint Skelly (NWS/PUB), Paul Schlatter (NWS/BOU), Michael Charnick (NWS/CYS, previously NWS/GJT)

GOES-15 began planned supplemental operations on Aug 4 to provide additional Eastern Pacific tropical cyclone support due to the operational impacts from the GOES-17 ABI Loop Heat Pipe anomaly (details here) This support is planned to continue through Sep 3. Given the coverage over the western US, the GOES-15 Imager also captured the intense wildfire activity, which allowed for comparisons with the newer GOES-17 ABI. Example comparisons between the two Imagers remind us of some of the improvements we have in wildfire monitoring with the GOES-R era satellites.

Starting with the 3.9 um SWIR imagery, abundant wildfire hot spots are diagnosed from both satellites across northern California on 08 Aug 2021 (Fig 1). However, the smaller/cooler fires that appear as faint hot spots in the ABI imagery, are very difficult to impossible to discern in the GOES-15 Imagery due to the poorer spatial resolution. The difference in temporal cadences is obvious, with the routine 5-minute imagery of the ABI allowing for smoother animations, for the ability to detect fires earlier, and for easier tracking of fire evolution with time. The image navigation from ABI is significantly better than that of GOES-15 at this point, with no noticeable movement from image to image. Finally, the saturation temperature in the ABI SWIR channel is much higher than previously.

A similar comparison is made between the VIS channels in order to observe the smoke plumes (Fig 2). In addition to those points referenced previously, the higher spatial resolution in the VIS makes clearer the areas of smoke including their source points, smoke edges, and development of pyrocu.

The 5-min ABI imagery shown above is from the routinely available CONUS sector. Of course, forecasters can request 1-min mesoscale imagery whenever desired, allowing for wildfire hot spots and smoke plumes to be detected even earlier, and tracked in more detail (Fig 3).

Bill Line, NESDIS and CIRA