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Helene’s genesis

Hurricane Helene spent time percolating in the northwestern Caribbean over the past week. The animation above show true-color imagery from the CSPP Geosphere site at 1-day intervals from 13 to 24 September. Convection over the southern Gulf of Mexico on 18-20 September moved northward and expanded greatly before being designated... Read More

GOES-16 True-Color imagery, daily at about 2050 UTC, from 13-24 September 2024

Hurricane Helene spent time percolating in the northwestern Caribbean over the past week. The animation above show true-color imagery from the CSPP Geosphere site at 1-day intervals from 13 to 24 September. Convection over the southern Gulf of Mexico on 18-20 September moved northward and expanded greatly before being designated a tropical storm at 1500 UTC on 24 September, shortly before the end of the stepped animation above.

Helene’s genesis was captured well by data from the direct broadcast antenna at AOML in Miami FL (link). The toggles below show GCOM-W1 AMSR-2 imagery at 36.5 and 89.0 GHz; the images are centered on the cyclone. The 89.0 GHz imagery, below, shows a strong signal of convective clouds shown in red. These cold features show up because 89.0 GHz energy is strongly scattered by ice. At all three times, curvature is apparent, but a definite center is not until the 1832 UTC imagery from 24 September.

GCOM-W1 AMSR-2 89.0 GHz observations over the tropical system that became Helene, 0652 UTC on 23 September, 0735 UTC on 24 September and 1832 UTC on 24 September (Click to enlarge)

The 36.5 GHz imagery, below, is more affected by cloud and rain water features below the freezing level. The background ocean shown to be very cold because ocean water has low emissivity at 36.5 GHz; energy is added to the upwelling signal from the cloud and rain droplets. For Helene, as it developed, this was mostly over the eastern half of the storm. By 1832 UTC on 24 September, there are pronounced curved bands near the center of newly-named Tropical Storm Helene.

GCOM-W1 AMSR-2 36.5 GHz observations over the tropical system that became Helene, 0652 UTC on 23 September, 0735 UTC on 24 September and 1832 UTC on 24 September (Click to enlarge)

Those in the southeast US should closely monitor the approach of Helene. For the latest on Hurricane Helene, and the multiple dangers it poses, refer to the National Hurricane Center.

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Fall Equinox 2024: There GOES Summer!

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... Read More

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.

GOES-East (GOES-16) Full Disk “CIMSS Natural Color” animation from June 20-September 22, 2024 at local sunset (23:00 UTC). Click to animate! (https://cimss.ssec.wisc.edu/satellite-blog/images/2024/09/GOES16_Solstice2Equinox2024_Sunset_CIMSSTrueColor_Logos.mp4)
GOES-West (GOES-18) Full Disk “CIMSS Natural Color” animation from June 20-September 22, 2024 at local sunrise (15:00 UTC). Click to animate! (https://cimss.ssec.wisc.edu/satellite-blog/images/2024/09/GOES18_Solstice2Equinox2024_Sunrise_CIMSSTrueColor_Logos.mp4)

Webapps about the Seasons

Screen shot of the webapp where one can explore the effect of the angle of incidence on sun’s energy. (Click on the image to go to the webapp.)
Explore the changing seasons on Earth by relating the orbit, rotation and solar insolation with this webapp by T. Whittaker. (Click on the image to go to the webapp.)

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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Aurora over Canada in the NOAA-21 Day Night Band

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... Read More

NOAA-21 VIIRS Day Night Band visible (0.7 µm) imagery, 0903 UTC on 12 September 2024 (Click to enlarge)

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.

NOAA-21 VIIRS Day Night Band visible (0.7 µm) imagery, 0722 UTC on 12 September 2024 (Click to enlarge)

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Lightning with Bebinca in the western Pacific

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... Read More

RealEarth LightningCast Display over Bebinca, 1650-1920 UTC on 11 September 2024, plotted over the Himawari-9 Band 13 (10.4 µm) imagery (Click to enlarge)

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.

JTWC Forecast Graphic for Tropical Storm Bebinca, 11 September 2024 (Click to enlarge)

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

Sea-surface temperatures and 200-850 mb wind shear, 1800 UTC on 11 September 2024 (Click to enlarge)

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.

Himawari Clean Window (Band 13, 10.4 µm) infrared imagery 1600-2030 UTC, 11 September 2024 (Click to enlarge)

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.

Total Precipitable Water fields over the western Pacific, 2000 UTC on 10 September – 1900 UTC on 11 September, 2024 (Click to enlarge)

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.

ASCAT Winds over Bebinca, 1122 UTC (Metop-B) and 1218 UTC (Metop-C) on 11 September 2024 (Click to enlarge)

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