The Fall Equinox in 2024 happened on September 22. According to the astronomical definition of the seasons, the autumnal (or fall) equinox marks the end of summer and the beginning of autumn, which lasts until the winter solstice (around December 21 or 22 in the Northern Hemisphere). This is the astronomical definition of the changing of seasons as the tilt of the earth on its axis will lead to summer in the southern hemisphere as we head into winter up here in the northern hemisphere.

The GOES satellites can provide a unique view of the earth as we pass through the various seasons. The angle of the shadow at sunrise or sunset (satellite time, or at the satellite nadir point) shows how earth progresses through the seasons from summer solstice to fall equinox. Watch the reflection of the sun (aka “sunglint”, the shiny spot which starts west of Mexico over the eastern Pacific in the GOES-East animation) migrate toward the equator over the course of summer; it ends up predictably right over the equator on the fall equinox.

Webapps about the Seasons

These images were made using NOAA data with geo2grid software, from UW-Madison, SSEC. T. Whittaker is thanked for the webapps.

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Day Night band visible imagery (0.7 µm) from NOAA-21 shows the characteristic signal of Aurora Borealis over southern Canada early in the morning (0722 UTC, below and 0903 UTC, above) on 12 September 2024 (Imagery is taken from the CIMSS VIIRS Imagery Viewer). Lunar illumination on 12 September was not present because the waxing gibbous moon was below the horizon. The light emitted from the Aurora, and from cities, and from various wildfire (for example, the Short Draw fire along the Wyoming/Montana border) is easily detected by the VIIRS imager in the view above. VIIRS has a bit more difficulty viewing the smoke plumes over the west, and the clouds with Francine over the mid-South, because of the relative lack of reflected light. The clouds from Francine are absorbing/scattering emitted light from cities in Louisiana and Mississippi making the city lights there less obvious.

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LightningCast probabilities (from this website) over the Central Dense Overcast of Tropical Cyclone Bebinca in the western Pacific to the northwest of Guam, above, show increasing values (the island of Guam is center bottom of the imagery above): magenta are values of 75%. Lightning activity within the central core is often a precursor to strengthening in a tropical cyclone, and the JTWC Forecast (below) for the system suggests just that.

Bebinca is over very warm SSTs and in a region of low shear. The projected path of the storm continues over warm water.

Himawari-9 Clean Window imagery, below (courtesy of the NWS Forecast Office in Pago Pago) overlain with lightning shows the cold cloud tops associated with the convection. Lightning becomes more common at the end of the animation, especially after 1800 UTC. This is in agreement with the LightningCast predictions shown above.

MIMIC Total Precipitable Water fields (source), below, show the spinup of the Tropical Storm. The circulation of this system continues to draw very moist air over the Marianas. The National Weather Service in Guam has issued Flood Watches, High Surf advisories and a wind advisory related to this event on 11 September.

Timely overpasses from Metop-B and Metop-C at around 1200 UTC on 11 September, shown below (from this site), helped benchmark the strength of the storm at that time.

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Francine became the 4th Hurricane of the Atlantic Tropical Cyclone season at 0000 UTC on 11 September (NHC advisory) 2024. The animation of True-Color imagery, above, from the CSPP Geosphere site, shows sporadic vigorous convection near the storm center in the hours before the hurricane designation.

The Gulf of Mexico can be monitored by the Direct Broadcast antenna at AOML in Miami. The toggles below show storm-centered 36.5 and 89.0 GHz brightness temperatures during the afternoon of 9 and 10 September. Radiation at 36.5 GHz has a big contribution from lower-level rain and cloud droplets, and the 2001 UTC/10 September imagery suggests little precipitation in the storm center. The 89.0 GHz brightness temperatures are affected by ice crystal distibutions.

Interests in/along the western and northern Gulf should closely monitor the progress of this storm. For more information on Francine, refer to the website of the National Hurricane Center. National Weather Service offices in Houston/Galveston, Lake Charles and New Orleans have local information on the storm.

Francine’s approach to the Louisiana coach is shown in the Mesoscale domain imagery below. NHC discussions noted the presence of dry air and shear (link) affecting the strength of the system, and that shear and dry air can be inferred by the ragged cloud pattern over the western half of the storm.

Francine made landfall in Terrebonne Parish at around 5 PM (2200 UTC) on 11 September (NHC Advisory).

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