Tropical Storm Laura south of Cuba

August 24th, 2020 |

GOES-16 4-panel display over Tropical Storm Laura, 0946 to 1621 UTC On 24 August 2020 (Click to animate); Upper Left: Band 13 “Clean Window” infrared (10.3 µm); Upper Right, Band 10 Low-level Water vapor infrared (7.3 µm); Lower Left: Band 2 Red Visible (0.64 µm); Lower Right, Day Convection RGB overlain with 5-minute aggregate GLM Flash Extent Density

Tropical Storm Laura’s path near/over the Greater Antilles has affected her strength, and the relative lack of organization means that night-time satellite identification of the center is a challenge. Consider the animation above. Northerly shear (analysis from this site) has shifted the coldest cloud tops to the south of the circulation center and with the 5-minute routine CONUS imagery, it is difficult to discern a surface circulation along the south coast of Cuba, where it was moving.  (A cluster of convection does appear there, although it is initially dwarfed in size by the convection to the south, south of 20 Latitude)

Visible imagery that becomes available at sunrise does show the center. The center gains prominence in the infrared as well as the convection to the south weakens. Note that the center can be discerned within the 1-minute shortwave infrared (3.9 µm) imagery from GOES-16 Mesoscale Sector 1: this link shows data from 0702 to 0803 UTC.  In the greyscale enhancement used in the linked-to animation, coldest cloud tops appear black and speckled because of a lack of precision at very cold temperatures in the 3.9 µm channel).

Sometimes, Day Night Band imagery from VIIRS can be useful in identifying tropical cyclone centers at night (see these 2016 examples with Matthew and Karl, for example). On the morning of 24 August, however, reflected moonlight was nil (Moonset over Cuba today was around 0500 UTC); in addition, the NOAA-20 overpass had Laura near the edge of the scan. Adaptive DNB imagery from Suomi NPP (just after 0700 UTC) and NOAA-20 (just before 0800 UTC), from the Direct Broadcast site at AOML in Miami, do show low clouds just south of Cuba, near the Jardines de la Reina, but it is a challenge to identify a surface circulation from this DNB imagery.

Suomi-NPP and NOAA-20 VIIRS Day Night Band Imagery at 0701 and 0752 UTC on 24 August 2020 (Click to enlarge)

Interests in Cuba and along the Gulf Coast of the United States should monitor closely the progress of Laura. Refer to the National Hurricane Center website for the latest forecasts.

Marco is sheared apart in the northern Gulf of Mexico

August 24th, 2020 |

GOES-16 Low-level Water Vapor Infrared imagery (7.34 µm), half-hourly from 0116 thorugh 1316 UTC, 24 August 2020, overlain with GOES-16 derived motion wind vectors at 250-350 mb (red) and Surface-900 mb (blue) (Click to animate)

Tropical system Marco (formerly a category 1 Hurricane) was weakened by shear overnight and early morning on 24 August (as forecast).  The half-hourly animation above, of GOES-16 Band 10, i.e., infrared “low-level” water vapor (7.3 µm), overlain with derived motion winds at upper (red) and lower (blue) levels (Click here to see only the water vapor animation;  here is the shear analysis from the SSEC Tropical website; Note in the animation how the number of low-level vectors increases greatly at the end of the animation as visible imagery becomes available at sunrise.  Also:  the shear in the eastern part of the domain, over the Florida Straits, suggests a favorable environment for Tropical Cyclone Laura, approaching western Cuba from the east) shows the effect of shearing.

Low level easterlies and upper-level southwesterlies mean that the vertical structure of the storm was interrupted:  the low-level circulation decoupled from the upper-level.   That is, the low-level circulation moved to the west as the mid- and upper-level parts of the storm moved north and east.  Result:  By sunrise, visible imagery (0.64 µm) showed the low-level swirl of the elongating near-surface circulation southeast of the mouth of the Mississippi River, and south and west of the main convection over and offshore of the northwest Florida panhandle.

GOES-16 Visible Imagery (0.64 µm) from Mesoscale Sector 2, 1129-1328 UTC 24 August 2020 (Click to enlarge)

For more information on Tropical Storm Marco, refer to the pages of the National Hurricane Center.

NUCAPS diagnoses of stable air near Tropical Storm Marco

August 22nd, 2020 |

GOES-16 ABI Band 13 Clean Window Infrared Imagery (10.3  µm) and NOAA-20 derived Gridded NUCAPS 850-500 mb lapse rates, 0656 UTC on 22 August 2020 (Click to enlarge)

Tropical Storm Marco over the northwest Caribbean Sea, shown above in a toggle of GOES-16 ABI Clean window imagery (10.3 µm) and a NUCAPS diagnosis of 850-500mb lapse rates, is over very warm waters and in a region of favorably low diagnosed vertical wind shear. (Wind shear is from this website, (direct link to shear); the product is described here)  An inhibiting feature in strengthening, as noted in the National Hurricane Center discussion, is stable air.

NOAA-20 overflew Marco shortly before 0700 UTC on 22 August, and NUCAPS soundings derived from CrIS and ATMS data on NOAA-20 showed the stable mid-tropospheric air surrounding the storm. The 850-500 mb lapse rates were around 5.5 C/km. (Gridded NUCAPS data can also be viewed here) Individual soundings over western Cuba and just off the northwest tip of the Yucatan peninsula also show the relatively stable air. (Click here to see the Lapse Rate Analysis overlain with NUCAPS Sounding Availability points from the AWIPS display)

Marco’s future path is forecast to move over very warm waters that are shown in the ACSPO analysis of SSTs, below, from Suomi-NPP VIIRS data.  Consult the National Hurricane Center for the latest on this storm that will likely affect the Texas/Louisiana Gulf Coasts.

Suomi-NPP ACSPO analysis of Sea Surface Temperatures, 0730 UTC on 22 August 2020 (Click to enlarge)

Using CSPP QuickLooks and Direct Broadcast data to view gridded NUCAPS fields

August 7th, 2020 |

NOAA-20 852-mb Temperatures, ca. 1750 UTC on 7 August 2020.  Inset:  Global Map of where the data sit (Click to enlarge)

A previous blog post (link) detailed how to access NOAA CLASS to create Gridded NUCAPS (NOAA-Unique Combined Atmospheric Processing System) imagery from those data.  (You can also view some gridded NUCAPS fields here;  click here to see the 850-mb field of Temperature from that site, it is very similar to the imagery above).   This post details how to use the CSPP QuickLooks software package to create imagery at different levels.  These QuickLook fields give good information quickly and at many different levels for Direct Broadcast data.

Download the Sounder QuickLook software for Linux from the CIMSS website here.  Documentation is also available at the download website.  The files to download are shown in this graphic. The package is self-contained and requires only unzipping and un-tarring.

After downloading, define the $CSPP_SOUNDER_QL_HOME variable as the directory where the package sits on your unix platform.  Then, set up the environment with the command:  source $CSPP_SOUNDER_QL_HOME/cspp_sounder_ql_env.sh.

This software package works on NUCAPS EDR (Environmental Data Records) files created at Direct Broadcast sites by CSPP (that are also available after some time from CLASS), and those files can be found at websites such as this one: ftp://ftp.ssec.wisc.edu/pub/eosdb/ — underneath this are directories for NOAA-20 (‘j01’) and Suomi-NPP (‘npp’). For example, NOAA-20 data from 7 August 2020 from the ~1747 UTC overpass is at ftp://ftp.ssec.wisc.edu/pub/eosdb/j01/crisfsr/2020_08_07_220_1747/ (This website is not preserved forever but will go away after about a week. The directory includes an edr subdirectory that contains the files needed; a typical filename looks like this:  NUCAPS-EDR_v2r0_j01_s202008071752319_e202008071753017_c202008071830250.nc; it is the EDR for NOAA-20 and it contains data on 7 August 2020 from 1752 through 1753 UTC. The directory will include up to about 18 of these EDRs (the number depends on how long the satellite is within view of the Direct Broadcast antenna at CIMSS).

How do you create the QuickLooks?

  1. Move the EDR files to your machine, and that’s easily done with wget ftp://ftp.ssec.wisc.edu/pub/eosdb/j01/crisfsr/2020_08_07_220_1747/edr/NUCAPS-EDR*.  Of course, the yyyy_mm_dd_jdy_hhmm value (2020_08_07_220_1747 above) changes with each satellite overpass!
  2. Create a list of the files in that directory, i.e., files=$CSPP_SOUNDER_QL_HOME/data/NUCAPS-EDR*
  3. Invoke the shell script from $CSPP_SOUNDER_QL_HOME/scripts/ql_level2_image.sh "$files" NUCAPS --dset temp --pressure 850.   This will create an image, shown above, that is a temperature mapping at the closest pressure level to 850 mb in the NUCAPS retrieval. (Pressure levels in the Radiative Transfer Model that is used by NUCAPS are listed here;  in the map label above, note that values are truncated, not rounded).  You can also map dewpoint temperature (dwpt), relative humidity (relh) and mixing ratio (wmix). By default, temperature scaling matches the bounds of the image, but you can specify the bounds if needed, using --plotMin=250.0 --plotMax=300.0, for example.  The time of the image is the time of the first scan line — for this ascending pass, it’s the southernmost line.  In this QuickLook image, the airmass difference between the relatively cool air over Ohio/Indiana and the warmer air to the south is apparent.

You can also create a QuickLook SkewT/logP plots for each scan. This produces one SkewT per ScanLine, at the mid-point along the scanline that contains 30 separate profiles.   The sounding below was produced by this command:

./ql_level2_skewt.sh ./data/NUCAPS-EDR_v2r0_j01_s202008071755119_e202008071755417_c202008071831450.nc NUCAPS

NOAA-20 NUCAPS Sounding from 1755 UTC on 7 August 2020 at 41.93º N, 75.81º W (Click to enlarge)

The SkewT has characteristics that suggest the presence of clouds.  What did this particular sounding look like in AWIPS?  That’s shown below.  In AWIPS, the sounding also terminated at about 550 mb, and the temperature and dewpoint lines above that level match the Quick Look sounding shown above.

NSharp AWIPS presentation of NOAA-20 NUCAPS Sounding at 41.93 N, 75.81 W at ~17UTC on 7 August 2020 (Click to enlarge)

NUCAPS Sounding Availability points from this NOAA-20 pass are shown below. The sounding point — in yellow — that is circled in blue is the one shown above. The sounding just to the east of that point — a green point that gives useful information down into the boundary layer — is shown here. Quick Looks choose the mid-point sounding along the line, and sometimes, as in this case, the retrieval that produced the profile did not converge.

NOAA-20 NUCAPS Sounding Availability Points from AWIPS, 1732 UTC on 7 August 2020 (Click to enlarge). The sounding shown above is from the point circled in blue.  This is in the middle of the 30 sounding points along the horizontal line of available profiles.