Daytime EUMETSAT Meteosat-10 High Resolution Visible (0.8 µm) images (above) showed Storm Daniel as it developed into a Medicane over the southern Mediterranean Sea on 09 September (with convective bands wrapping around the storm center), then moved inland across northeastern Libya on 10 September 2023.

Hourly MIMIC Total Precipitable Water images from 09 to11 September (below) displayed bands of TPW in the 2.0-3.0 inch range (darker shades of red) wrapping around the center of Storm Daniel as it moved inland — causing heavy rainfall and extensive flooding (see this Climate Connections blog post for more details). Ship reports indicated that water temperatures in the central Mediterranean Sea — where Storm Daniel had meandered for a few days before approaching Libya — were in the 77-79ºF range.

As the center of Storm Daniel was approaching the Libya/Egypt border on 11 September, a MIMIC Total Precipitable Water image with an overlay of Metop-C ASCAT surface scatterometer winds at 0800 UTC showed a long fetch of winds in the 25-33 knot range (red barbs) approaching the coast of Libya — then at 1100 UTC, a ship report within the same region of that ASCAT fetch reported a wind speed of 40 knots (below).

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5-minute PACUS Sector GOES-18 (GOES-West) Shortwave Infrared (3.9 µm) and SO2 RGB images (above) showed the thermal anomaly (heat signature) and a plume of SO2 (brighter shades of cyan) for 1.5 hours following the onset of an eruption of Kilauea on the Big Island of Hawai`i late in the day on 10 September 2023.

The Kilauea eruption began at 0115 UTC on 11 September (3:15 PM HST on 10 September) — and about 15 minutes later, the GOES-18 3.9 µm Shortwave Infrared brightness temperature sensed at the volcano summit reached 137.88ºC (below) — which is the saturation temperature of GOES-18 ABI Band 7 detectors.

GOES-18 True Color RGB + Nighttime Microphysics RGB images from the CSPP GeoSphere site (below) displayed the volcanic plume as it moved southwest; the Kilauea summit’s thermal anomaly appeared as darker blue pixels in the final (0411 UTC) Nighttime Microphysics RGB image of the animation.

A longer animation of larger-scale GOES-18 Shortwave Infrared and SO2 RGB images (below) revealed the continued southwest transport of the SO2 plume for about 10 hours post-eruption. The GOES-18 Shortwave Infrared brightness temperature sensed at the Kilauea summit remained at the aforementioned 137.88ºC saturation temperature for nearly the entire time period shown.

A Suomi-NPP VIIRS Day/Night Band (0.7 µm) image valid at 1247 UTC or 2:47 AM HST (below) showed a large bright signature over the Kilauea area, due to the intense glow of the volcanic lava flows. The VIIRS instrument was scanning from NW to SE; note the dark streak extending SE of the bright Kilauea glow, which was a hysteresis effect due to the sensor becoming saturated by the intense volcanic signature.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed Lee as it intensified to become a Category 1 Hurricane in the Central Atlantic Ocean on 06 September 2023. The coldest cloud-top infrared brightness temperatures were around -90C (brighter white pixels embedded within darker black areas). 

Lee had been moving across warm water — and was traversing an environment having low deep-layer wind shear (below) — factors which were favorable for intensification. Water temperature and wind shear imagery was sourced from the CIMSS Tropical Cyclones site.

Meanwhile, in the East Pacific Hurricane Jova rapidly intensified to a Category 4 storm by 2100 UTC on 06 September, exhibiting a pinhole eye as seen in GOES-18 (GOES-West) Visible and Infrared imagery (below).

Similar to Lee, Jova had been moving across warm water — and was traversing an environment having low deep-layer wind shear (below) — factors which were favorable for intensification.

Jova was later upgraded to Category 5 intensity at 0900 UTC (Infrared images: animated GIF | MP4). 

===== 07 September Update =====

At 0300 UTC on 08 September, Hurricane Lee was upgraded to a Category 5 storm (the first Category 5 of the 2023 Atlantic Basin season). 6 hours of 1-minute GOES-16 Infrared images leading up to that time are shown above — and the 0100 UTC Infrared image with an overlay of Metop-C ASCAT surface scatterometer winds is shown below. Note: 25-km resolution ASCAT winds are available in AWIPS, which indicated a maximum speed of 75 knots — however, the Ultra-High Resolution (UHR) ASCAT wind product at that time (source) had a maximum speed of 136 knots.

Even though deep-layer wind shear was gradually increasing in its vicinity, Lee reached Category 5 intensity as it began to move across water with increasing values of Ocean Heat Content and Sea Surface Temperature (below).

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Northeastern Minnesota, northwestern Wisconsin and the adjacent waters of Lake Superior experienced severe weather late on 5 September 2023. The animation below shows the strong convection moving over western Lake Superior. GOES-16 Mesoscale Sector 1 imagery from 2300-2359 UTC shows numerous convective towers bubbling up and collapsing. Storm Reports from SPC include a 2315 UTC report of a 61-knot gust from the ship Dirk S. VanEnkevort 25 miles southeast of Lutsen (satellite image at that time; note the overshooting top!).

The Storm Prediction Center had a Slight Risk over the western Great Lakes on the 5th, consistently from the 1200 outlook through the 2000 UTC outlook. Watch box #669 was issued for the region at 2100 UTC; the primary threat was strong winds and hail. See also SPC”s Mesoscale Discussions 2084 and 2087 on that day.

The Plains were under the influence of an Elevated Mixed Layer (EML) on this day, as shown in the GOES-16 Band 10 (Low-level water vapor) infrared animation below; EMLs in this enhancement are dark red. The 1200 UTC sounding from Topeka (here, or here), shows very steep mid-level lapse rates as expected with an EML. That is the type of airmass moving northeastward towards Lake Superior during the day.

The upper-air station at Chanhassen MN released a balloon at 1800 UTC, and the toggle below shows the airmass change between 1200 and 1800 UTC on the 5th: the atmosphere moistened and destabilized in those 6 hours. Notice that the shear has changed as well.

Upper-air information with better time resolution was available 5 September for the Minneapolis airport from ACARS data, as shown below. On this day however, no water vapor information was available, so the erosion of the dry layer that is apparent in the two soundings above is not sampled.

NOAA-20 overflew the region shortly after 1800 UTC on 5 September. NUCAPS profiles derived from CrIS and ATMS data on board NOAA-20 could be used to diagnose the thermodynamics of the atmosphere at the time. The image below shows lapse rates (850-700; 700-300) and the Total Totals index; all parameters show a corridor of reduced stability stretching from south-central Minnesota up to western Lake Superior. Quality Flags show green, many complete infrared retrievals, in this region, as might be expected from the visible satellite image. Data from both GOES and JPSS satellites suggest strong convection is possible.

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The slider below compares the 2349 UTC visible imagery with SAR winds derived from RCM3 Normalized Radar Cross Section (NRCS) observations. Note that SAR wind observations over land (including the Apostle Islands) are not valid. Numerous wind maxima in the 25-30 m/s range are apparent in the region of convection extending northeast of the Apostle Islands.

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Thanks to Patrick Ayd, Science and Operations Officer at WFO Duluth, for alerting us to this very interesting event!

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