Hurricane Hilary, off the coast of Mexico, is forecast to move northward into the southwestern United States, becoming a rare instance of a tropical cyclone affecting California. The 1200 UTC imagery on 18 August 2023 above shows a well-defined eye, with warm sea-surface temperatures (SSTs) in the Pacific Ocean along the storm path until the storm reaches 25^oN, the latitude of central Baja California. (Sea Surface temperatures in the shallow northern Gulf of California are even warmer, near 90^oF, white in the enhancement used.). Steep topography along the Baja California peninsula and cold SSTs north of 27^oN latitude will both affect the strength of the storm as it moves northward.

A  Mesoscale Domain Sector was positioned over Hilary, providing imagery at 1-minute intervals — Visible images, below, revealed low-level mesovortices within the eye of the Category 4 hurricane. 

Metop-C overflew Hilary at about 0500 UTC on 18 August 2023 (link), and Advanced Scatterometry winds from that time, below, show tropical storm-force winds extending about 200 miles to the northeast of the system center.

GOES-18 Airmass RGB imagery below, hourly from 0020-1420 UTC on 18 August, shows Hilary off the coast of Mexico, and also a slowly-moving cyclonic circulation off the coast of California, a circulation that will help guide Hilary towards a projected landfall in northwestern Mexico/the southwestern USA.

Imagery from the SSEC/CIMSS Tropical Weather website, below, shows the storm path, SSTs and current shear along the forecast path (favorable now, progressively less favorable into the weekend) and the 700-200 mb steering flow.

Interests in northwest Mexico, the Baja peninsula and the southwestern United States should pay close attention to this storm through the weekend into early next week. An important hazard will be flooding. MIMIC Total Precipitable Water fields, below, for the 24 hours ending at 1400 UTC on 18 August, show the moisture associated with the hurricane.

The latest information on Hilary is available at the National Hurricane Center and the National Weather Service Offices in San Diego, Los Angeles, Hanford (the San Joaquin valley), Phoenix and Las Vegas.

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1-minute Mesoscale Domain Sector GOES-18 (GOES-West) “Red” Visible (0.64 µm) + Fire Power derived product (a component of the GOES Fire Detection and Characterization Algorithm FDCA), Shortwave Infrared (3.9 µm), “Clean” Infrared Window (10.3 µm) and Cloud Top Temperature derived product images (above) showed that the Crater Creek Fire — located in far southern British Columbia, less than 10 miles from the Washington border — produced a pyrocumulonimbus (pyroCb) cloud late in the day on 16 August 2023.

Beginning at 0023 UTC (prior to pyroCB development), the fire occasionally exhibited 3.9 µm brightness temperatures of 137.88ºC (the saturation temperature of the GOES-18 ABI Band 7 detectors) — and Fire Power values reached 3929.32 MW at 0142 UTC (above). Cloud-top 10.3 µm brightness temperatures first reached the -40ºC pyroCb threshold (shades of blue) at 0035 UTC — and later cooled to a minimum of -42.31ºC (with a corresponding Cloud Top Temperature of -57.17ºC) at 0157 UTC (below).

1-minute GOES-18 True Color RGB images from the CSPP GeoSphere site (below) showed the abrupt pyroCb pulse as it quickly rose above the wildfire smoke plume, and the pyroCb anvil as it then drifted north-northeastward.

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10-minute Full Disk GOES-18 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed clusters of convection that moved west-southwestward across Alaska’s Seward Peninsula on 11 August 2023.

Beginning at 2300 UTC, a Mesoscale Domain Sector was positioned to cover western Alaska — providing images at 1-minute intervals (below).

A cursor-sampled METAR report from Tin City, Alaska (PATC) at 2324 UTC (below) indicated that a heavy thunderstorm with rain (+TSRA) was occurring at that time.

 

A cursor-sampling of GOES-18 10.3 µm infrared brightness temperature, Cloud Top Temperature derived product and Cloud Top Height derived product at 2324 UTC (above) revealed vales of -53.37ºC, -57.24ºC and 32953 ft, respectively. Note that these values were sampled for convective cloud tops that appeared to be located about 20 miles NW of Tin City, over open water — but this was taking parallax into account, which can be significant at higher latitudes (below).

While summertime thunderstorms are common across much of Interior Alaska, a heavy thunderstorm over the far western portion of the Seward Peninsula is rather rare.

Just a heavy thunderstorm at, checks notes, Tin City, Alaska – along the Bering Sea coast, less than 60 miles from mainland Russia. With multiple decades of observations, this is only the 2nd instance of a heavy thunderstorm at Tin City (Aug 7, 2013). ?? pic.twitter.com/iqpEUh84Fj

— Brian Brettschneider (@Climatologist49) August 12, 2023

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SSEC Satellite Data Service is using McIDAS-X and HereGOES software packages to create imagery from the GOES-R Solar Ultra-Violet Imager (SUVI) instrument that monitors solar ultraviolet activity. Realtime SUVI images from both GOES-16 and GOES-18 can be viewed with the SSEC Geo Browser.  Rick Kohrs at SSEC created the imagery in this blog post by loading images at different times, i.e., time-shifted by 2 hours. The animation above (three-dimensionality is achieved if the user crosses their eyes and focuses on the image that appears in the middle) shows data from the GOES-16 SUVI at 171 Å, from 1700-1900 UTC on 10 August 2023. A second animation, below, requires the use to don red/green glasses to perceive the three dimensions.

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