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.

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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.

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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.

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

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True-color imagery from the CSPP Geosphere site, above, is annotated to identify a wildfire in progress. This is one of several fires over Oregon, as evidenced by the widespread smoke that is present across the region. The animation below, shows the evolution during the day of the fires. Pyrocumulonimbus (PyroCB) clouds — with lightning (see below) — developed over the fires.

Lapse rates derived from NUCAPS profiles, below, show a large region of near-dry adiabatic conditions (between 7 and 9^o C/km) over much of central Oregon where the convection developed. And individual NUCAPS profile, from 44.3^oN, 122^oW, below, shows an atmosphere at that point that will not greatly suppress vertical motions. The Equilibrium Level (EL) is diagnosed to be at the Tropopause.

GOES-18 Derived Stability Index values of CAPE (clear sky only) from 0300 UTC on 8 September 2024, plotted with 3.9 µm brightness temperatures and fire radiative power show instability over eastern Oregon and fire signatures.

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If you know the area you are monitoring has active fires, and satellite data is telling you the overlying atmosphere is nearly unstable, what might you expect from NGFS displays? The RealEarth NGFS display is shown below, at hourly timesteps from 1700 UTC 7 September through 0100 UTC 8 September. (Here is a speedier animation.) Note the presence of LightningCast probability contours (and GLM observations). NGFS detections — in red and orange — show an increase in Fire Radiative Power. Thunderstorms develop to the west of the fire; subsequently a pyroCB develops over the main fire (GLM FED at 0014 UTC shows lightning). This is the kind of information that is useful for Fire Weather Decision Support.

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GOES-18 Visible imagery, above, over the Samoan Islands, shows a variety of cloud structures moving from north to south over the Samoan Islands, especially over the smaller islands of American Samoa (Tutuila, Ofu/Olosega and Ta’u). The animation below, covering about the same time span, shows GREMLIN radar estimates. GREMLIN is a Machine-Learning tool the predicts radar returns based on ABI and GLM observations. Although it was trained on CONUS imagery, it does provide actionable information over the tropical South Pacific.

The view to the east of the Pago Pago airport, above, at 2127 UTC, shows the lower ceilings associated with the heavy rain. GREMLIN did a great job on this day of predicting onset and cessation of rains during a day when Flash Flood Warnings were issued (at 2208 UTC).

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A second Flash Flood warning was issued later in the day, and the run-up to that warning is shown in the animation below, visible imagery from 0050 to 0240 UTC on 7 September, below, and GREMLIN imagery from 0040 to 0230 UTC, at bottom.

The Forecast Office in Pago Pago had a Facebook post (below) that included one of the GREMLIN images above highlighting a Flash Flood warning issued at 0249 UTC on 7 September.

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Thanks to Jane Allen and Dora Meredith, NWS Pago Pago, for the AWIPS imagery!

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The radiosonde profile from the balloon launch just before 0000 UTC 7 September, above, (imagery from the Wyoming Sounding site), shows a very moist airmass, with saturation from the surface up to 400 hPa, and relative dryess above that level. Total Precipitable Water was 63 mm.

NOAA-20, NOAA-21 and Metop-C all provide NUCAPS (NOAA-Unique Combined Atmospheric Processing System) profiles. The Metop-C overpasses near American Samoa at 1842 UTC on 6 September, shown below, include a series of four green points (that is, points where the infrared retrieval converged to a solution) in the westernmost column of profiles just east of the Samoan Islands. The NUCAPS profile below is similar to the observation from Tutuila: very moist (this one had a Precipitable Water value of more than 2″), and a dry region above 400 hPa. NUCAPS profiles can give useful thermodynamic information in regions where conventional data are missing.

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At 0000 UTC on 9 September, the upper-air sounding, below (source), shows a much drier atmosphere. Note, for example, that Total Precipitable Water is 45.7mm on 9 September compared to 63mm on the 7th.

The NUCAPS profile (from Metop-C), at 2054 UTC on 8 September, below, centered on Tutuila (the island on which Pago Pago sits) shows structures that are similar to the rawindsonde above, namely relatively moist from 500-300 mb with dryer air above and below. It is always important to remember that NUCAPS moisture resolution is about 4-6 layers in the troposphere.

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