Overnight in the eastern Indian ocean, a tropical storm underwent significant deepening to become Severe Tropical Cyclone Zelia. The name “tropical cyclone” might make one think of a comparatively weak storm compared to a hurricane, but that is because the names of these systems vary depending on the part of the world they take place. There’s no functional different between a hurricane, typhoon, or severe tropical cyclone, just a different ocean basin where they can be found. The category rankings are the same for all tropical cyclones, and as of sunrise on 13 February, it had become a Catergory 4 storm, with winds over 209 km/h (130 mph). Forecasts from the Australian Bureau of Meteorology indicate that it will continue to strengthen to a Category 5 system before taking a sharp left hand turn and heading south. Zelia is currently lashing the coast with winds and rain as it strengthens, and because of some locations will be under this system for many hours, some rainfall forecasts are in excess of 50 cm (20 inches).

The rapid development of an eye can be seen in the following loop of Band 13 (10.4 microns, the infrared window) from the Advanced Himawari Imager (AHI) aboard Japan’s Himawari-9 geostationary satellite, . Because this eye development took place in the nighttime hours, visible-wavelength imagery cannot be used to observe this process. Longtime viewers of tropical cyclone imagery might be slightly started to see Zelia spinning in a clockwise direction, but that’s expected for a Southern Hemisphere cyclone.

This strong intensification is not unexpected given the extremely warm sea surface temperatures found just northwest of Australia. The NESDIS High Resolution Sea Surface Temperature analysis (available from SSEC’s Real Earth) shows temperatures at or above 25 C (over 77 F), which contribute substantially to the latent heat processes needed for tropical cyclone development and maintenance.

For the latest updates, be sure to check the BOM’s Tropical Cyclone website.

 ===== 14 February Update =====

2.5-minute Target Sector JMA Himawari-9 Visible and Infrared images (above) showed that Zelia made landfall along the coast of Western Australia (near Port Hedland) not long before 0500 UTC on 14 February. Cloud-top infrared brightness temperatures in the eyewall region were in the -80 to -85ºC range (shades of violet to purple).

A Suomi-NPP VIIRS Day/Night Band image (below) provided a high resolution view of the cloud-filled eye of Zelia, shortly after the tropical cyclone made landfall.

In a ~2 day animation of 2.5-minute Himawari-9 Infrared images (below), it was apparent that Zelia remained generally quasi-stationary for an extended period on 12-13 February — and as mentioned in a Joint Typhoon Warning Center discussion, this led to a wind-induced upwelling of cooler sub-surface water beneath the Category 4 intensity tropical cyclone (which likely played a role in reducing further intensification). The images include surface plots from Port Hedland (YPPD), which reported a wind gust of 65 knots at 0700 UTC. Also of note: during much of the day on 12 February, thunderstorms moving inland across the Port Hedland region exhibited cloud-top infrared brightness temperatures as cold as -90 to -95ºC (shades of yellow to gray, embedded within darker purple areas) — these thunderstorms were producing periods of heavy rain (YPPD METARs).

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10-minute Full Disk scan Dust RGB images from GOES-18 (GOES-West), GOES-17, GOES-19 (Preliminary/Non-operational) and GOES-16 (GOES-East) created using Geo2Grid (above) showed vivid signatures of blowing dust (brighter shades of magenta) that originated over parts of northern Mexico and southwestern New Mexico — and was subsequently transported northeastward across southern New Mexico and southwestern Texas on 11th February 2025.

The respective satellite locations over the Equator are: GOES-18 (137.0 W longitude), GOES-17 (104.7 W longitude), GOES-19 (89.5 W longitude) and GOES-16 (75.2 W longitude). However, GOES-17 has been temporarily brought out of storage and is drifting slowly from 12th-15th February 2025, approximately 0.3 degrees of longitude in total. All ABI imagery during this “Longitude Test” will be resampled to the nominal 105 W location. GOES-17 products will be analyzed for any potential impacts that this shift in longitude might cause. The overall goal of the Longitude Test is to determine what product impacts (if any) there might be when GOES-16 (currently operational as GOES-East) is moved to 75.5 W in March, ahead of GOES-19’s arrival (GOES-19 is then scheduled to become operational as GOES-East on 4th April). Tangentially, this also tests our ability to track a GOES-R series satellite as it moves (and still receive data).

5-minute CONUS Sector GOES-16 daytime True Color and Nighttime Microphysics RGB images from the CSPP GeoSphere site (below) highlighted the hazy tan-colored appearance of the blowing dust during the hours leading up to sunset, followed by the brighter shades of magenta dust signature at night (the Nighttime Microphysics RGB makes use of the 10.3-12.3 µm “Split Window Difference“, which is effective for dust detection).

A GOES-16 Visible image (below) included plots of the strong winds that were creating the blowing dust — which at that time was restricting the surface visibility to 1/2 mile at El Paso, Texas (KELP).

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One of the first things that meteorologists learn in their Intro to Weather class is that low pressure means cloudy skies and rain while high pressure means clear skies and sun. Of course, the second thing that meteorologists learn is that weather often doesn’t behave in a textbook way. The southeastern United States today is a good example of that.

Looking just at the surface observations from the Weather Prediction Center, one would think that the Atlantic southeast is under fairly quiescent conditions. A strong high pressure system is centered over southeastern Pennsylvania, but an arm of this high extends south all the way into northeastern Georgia. A stationary front parallels the northern border of Florida. Even the low pressure system in northern Mississippi is quite weak, with a central pressure that is higher than the average mean sea level pressure. All in all, it looks to be a fairly ordinary day.

But the satellite on SSEC’s Real Earth tells a different story. Here’s a loop of true color imagery from GOES-16 this morning.

Obviously, the Atlantic southeast is dominated by clouds, which seems to stand in opposition to what the surface map indicates should be happening. Some of the cloudiness is due to overflow from the midwestern cold front. But a good deal of the cloudiness is caused by the cyclonic flow around the high pressure in the northeast. The flow is coming from over the ocean, where is becomes laden with moisture. As it moves ashore, it runs into the southern extend of the Appalachian Mountains where orographic uplift forces it aloft and clouds and rain ensue.

One of the localized phenomena that arises from this kind of flow in northeastern Georgia has been dubbed the “wedge.” In wedge events, a shallow, stable layer of cold air forms due to cold air damming against the Appalachians. A sounding from the 1500 UTC RAP analysis shows this clearly:

This time of year is historically home to the strongest cold air damming events in this region, and their effects can be significant. Low level inversions like the one seen today can contribute to hazardous wintertime precipitation like freezing rain, as snow formed in a saturated layer aloft melts as it falls through the elevated warm layer then freezes again when it contacts the surface. In April 2023, a wedge event received national attention: the Masters golf tournament was interrupted by a backdoor cold front that formed from the wedge of cold air flowing southward along local terrain. During that event, winds exceeded 30 mph, trees were felled near spectators, and play was interrupted due to these hazardous conditions.

Days like today are a reminder that it’s always a good idea to get a bird’s-eye view of the weather using the wealth of observations that satellites can provide.

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GOES-16 (GOES-East) Upper-level Water Vapor (6.2 µm) and Mid-level Water Vapor (6.9 µm) images (above) displayed leeside cold frontal gravity waves (reference) as they propagated southward across Oklahoma, Texas and far eastern New Mexico on 8th February 2025.

In a corresponding animation that included plots of surface wind barbs, peak wind gusts and frontal analyses (below), it could be seen that the gravity waves were generally present along or just behind the western portion of the surface cold front — while farther to the east, the gravity waves advanced ahead of the cold front.

Plots of GOES-16 Water Vapor (6.2 µm / Band 08 and 6.9 µm / Band 09) Weighting Functions derived using rawinsonde data from Fort Worth, Texas (KFWD) (below) indicated that the peak contribution of upwelling radiation for both spectral bands was originating from the middle troposphere (at pressure levels of 516-460 hPa) — with no contributions from the surface.

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The leeside cold frontal gravity waves were also apparent in GOES-19 (Preliminary/Non-operational) Upper-level Water Vapor (above) and Mid-level Water Vapor images (below).

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