It is mid to late July, and the western Pacific Ocean is starting to see its share of tropical activity. While Tropical Storm Francisco is spinning toward the Ryuku Islands of southwestern Japan, the people of Guam have their eyes on Invest 98W, an intensifying system closely approaching their island. As of 0900 UTC on 23 July 2025, Invest 98W is exhibiting winds between 18 and 23 kts. However, the Joint Typhoon Warning Center is projecting a high potential for this system to intensify to a tropical cyclone within 24 hours. Initial satellite imagery using Band 13 (the infrared window) from the Himawari-9 Advanced Himawari Imager (AHI) shows the system as of 1900 UTC on the 23rd. This can be seen on SSEC Real Earthas the group of cold brightness temperatures (therefore deep convection) between 10 and 15 deg N and 140 and 150 deg W.

Note that the invest does not appear to have the clear cyclonic circulation of a more developed tropical storm like what can be seen in Tropical Storm Francisco in the northwest part of the image. However, low leevl winds resolved by scatterometry indicate that a circulation is in place just ot the southwest of Guam.

The biggest concern for Guam right now is significant rainfall. Satellite imagery can help tell that story by indicating the large quantity of water vapor available for precipitation. The AHI Band 8 (6.2 microns) shows large regions of cold brightness temperatures in yellow, indicating dep layers of the atmosphere with high water vapor content.

This can be further seen in the CIMSS MIMIC-TPW2 product, which quantifies the total precipitable water through compositing microwave imagery from several different polar orbiting satellites. While MIMIC does not have the temporal resolution of the geostationary orbiter, its innovative morphological compositing technique is still able to produce hourly observations. The microwave instruments are able to penetrate the upper level clouds and thus the cyclonic circulation of Invest 98W is more readily apparent. This product shows that TPW values near Guam are exceeding 70 mm.

These high values for water vapor are going to contribute to significant rainfall totals for Guam in the coming days. The Global Ensemble Forecast System (GEFS) has 21 members and gives a general assessment of the breadth of potential forecast outcomes over the next week. While the mean outcome is a total of 4 inches of rain and the greatest clustering is between 2 and 3 inches, individual members are showing anywhere between 2 and 14 inches of rainfall between the 23rd and the 31st of July.

More information about this system can be obtained from the Joint Typhoon Warning Center at https://www.metoc.navy.mil/jtwc/jtwc.html.

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5-minute PACUS Sector GOES-18 (GOES-West) daytime True Color RGB and Nighttime Microphysics RGB images created using Geo2Grid (above) revealed the cyclonic circulation of a Mesoscale Convective Vortex (MCV) that migrated west-northwestward across southern Arizona into southeast California (not far south of the California/Nevada border) during the 2-day period from 16 July to 18 July 2025. This MCV emerged from a dissipating cluster of thunderstorms over far southeast Arizona after about 0900 UTC on 16 July — and was moving through an environment of enhanced moisture and instability that was favorable for additional convective development.

This MCV was highlighted in NWS/WPC Mesoscale Precipitation Discussions on 16 July, 17 July and 18 July — since this middle-tropospheric feature was helping to force the development of new thunderstorms, further enhancing flash flooding risks in the vicinity of the MCV.

GOES-18 Shortwave Infrared images visualized using RealEarth (below) included outlines of the numerous Flash Flood Watches/Advisories/Warnings that were issued as the MCV propagated from southern Arizona to southeast California.

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1-minute Mesoscale Domain Sector GOES-18 (GOES-West) GeoColor RGB images with an overlay of Next Generation Fire System (NGFS) Fire Detection polygons (above) showed the rapid growth of the Cram Fire in central Oregon during the day on 14 July 2025. Strong westerly winds helped to transport a dense veil of smoke eastward. This wildfire had started on the previous day, but exhibited extreme behavior on 14 July — growing to 10000 acres, and forcing some evacuation orders to be issued.

1-minute GOES-18 Visible images with an overlay of the FDCA Fire Mask derived product (below) also displayed the large thermal signature of the Cram Fire as it burned in the vicinity of the Wasco/Jefferson County line. Data from RAWS sites showed that winds just northeast of the fire were gusting as high as 40 mph at 2300 UTC.

An overpass of Landsat-9 provided a 30-meter resolution image of the Cram Fire at 1844 UTC on 14 July, viewed using RealEarth (below). The active fire front appeared as brighter shades of pink, with the burn scar exhibiting darker shades of orange-brown.

Several hours after sunset, a NOAA-20 VIIRS Day/Night Band image (below) displayed the bright nighttime glow of the Cram Fire (located between Antelope and Madras)  — both the northern and southern flanks of the wildfire were still actively burning at that time.

===== 15 July Update =====

After the overnight southward passage of a cold front, a transition to north-northeast winds began to transport dense wildfire smoke southwestward and southward on 15 July (above) — with this smoke occasionally reducing the surface visibility to 4 miles at Madras and 1.75 miles at Redmond. The Cram Fire continued its trend of very rapid growth, burning an area over 28000 acres by late morning, increasing to over 64000 acres by the end of the day (remaining 0% contained); evacuation orders were expanded as a result. In addition, Highway 97 near Willowdale was briefly closed early in the day, due to the close proximity of the fire (and its dense smoke creating hazardous driving conditions).

With RAWS sites surrounding the fire reporting N-NE wind gusts in the 25-30 mph range, the GOES-18 Fire Mask (below) showed that most of the burning activity shifted to the southern flank of the Cram Fire as the day progressed. The large burn scar exhibited darker shades of gray in the Visible imagery.

A toggle between NOAA-20 VIIRS Day/Night Band images during the post-sunset nighttime hours on 15 July and 16 July (below) showed a notable south-southwestward shift in the larger, more active fire front along the Cram Fire southern flank.

Toggles between VIIRS Day Fire RGB images from NOAA-20, NOAA-21 and Suomi-NPP on 14 July and 15 July (below) also showed the dramatic increase in fire size within ~24 hours. Areas of active fires showed up as brighter shades of red, while the burn scar appeared as darker shades of reddish-brown.

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10-minute Full Disk scan GOES-19 (GOES-East) Infrared images combined with the Fire Mask derived product (above) showed a wildfire in western Ontario (north of Red Lake, CYRL) that produced a large pyrocumulonimbus (pyroCb) cloud beginning at 1930 UTC — when cloud-top infrared brightness temperatures first reached -40ºC, darker shades of blue — on 10 July 2025. The wildfire was intensifying in advance of an approaching warm front (SW winds at Red Lake were gusting to 19-20 knots).

The pyroCb — which eventually merged with other nearby meteorological thunderstorms — exhibited cloud-top infrared brightness temperatures as cold as -67.75ºC at 2150 UTC (above).

In a plot of rawinsonde data from Pickle Lake, Ontario (CYPL) at 0000 UTC on 11 July (below), the -67.75ºC cloud-top temperature corresponded to an overshoot of the Equilibrium Level (EL) / Tropopause of nearly 1 km.

This pyroCb cloud produced a notable amount of lightning (beginning at 1950 UTC), as seen from overlays of GOES-19 GLM Flash Extent Density and Flash Points (below).

A toggle between NOAA-21 VIIRS GeoColor RGB images (with an overlay of NOAA-21 VIIRS Fire Radiative Power) at 1755 UTC and 1943 UTC is shown below (source). The later image displayed the pyroCb cloud shortly after its formation, as it had begun drifting eastward away from the large wildfire.

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