Sea Breeze Convergence Convection over South Florida

 In accordance with Mesoscale Discussion #708 issued by NWS/Storm Prediction Center at 1638 UTC, the main area of focus for thunderstorm downburst wind generation was set as the south Florida region surrounding the sea breeze convergence zone. Figure 1 shows the primary area of concern for severe downburst winds positioned along the south Florida Atlantic coast. As shown in Figures 2 and 3 below, this region is characterized by strong ambient instability, creating a highly favorable thermodynamic environment for robust convective updrafts. Furthermore, the convergence of lingering thunderstorm outflow boundaries with the eastward-advancing sea-breeze convergence zone front serves as a potent mesoscale lifting mechanism. Figures 2 and 3 show good agreement in sounding profile structure and downburst potential between the GOES-19, RAP model, and RAOB soundings in the Miami, FL area.

Figure 1: Composite of SZA day cloud convection, LightningCast lightning probability, and MRMS radar reflectivity at 2018 UTC 12 May 2026.

Figure 2. GOES-19 sounding profile near Miami, FL at 1800 UTC compared to an eastern U.S. sector IR BTD product image during the afternoon of 12 May 2026.

Figure 3. Comparison of the Miami, FL RAOB profile to the RAP model analysis sounding profile in the Miami, FL area at 1800 UTC 12 May 2026.

StormRangerWX

FCI WVT Imagery

 One of the products demonstrated at this year’s HWT is synthetic water vapor transmittance (WVT) imagery.  The product, a ratio of 0.91 μm to 0.86 μm reflectances, is based on the existence of water vapor absorption at 0.91 μm.  Dividing by 0.86 μm helps to highlight the water vapor signature.  As NOAA does not yet operate a satellite channel at 0.91 μm, synthetic imagery is created for HWT from the High-Resolution Rapid Refresh model run through the Community Radiative Transfer Model.  However, EUMETSAT’s latest geostationary satellite, Meteosat-12, does contain 0.91 μm and 0.86 μm channels on its Flexible Combined Imager (FCI), and is used to augment the synthetic imagery during HWT.

Figure 1 shows an FCI WVT loop over northeastern Africa and the Arabian Peninsula from 12 May 2026.  The darker regions are indicative of higher amounts of total precipitable water (TPW).  Noteworthy regions of higher TPW can be seen along the west and south coasts of Saudi Arabia and Yemen as moisture moves onshore from the Red Sea and the Gulf of Aden.  The greater moisture along and equatorward of the Sahel is also very apparent.  The high spatial and temporal resolution afforded by the satellite imagery allows for very accurate monitoring of water vapor during the day in clear regions.

Figure 1: Half hour Meteosat-12 FCI WVT imagery from 0920 UTC to 1150 UTC 12 May 2026 over northeastern Africa and the Arabian Peninsula.

Viewing Low-Level Features With MesoAnywhere

 There wasn’t much convection today over the MFL CWA, so I spent a lot of time looking at MesoAnywhere to see how it performs compared to the Day Cloud Phase Distinction RGB from both CONUS scale and meso sector 1.

Some sort of boundary was evident on radar extending southwest from an area of showers west of the Miami radar.

Figure 1- Radar image from KAMX radar showing a boundary extending away from an area of showers.

I wanted to see if this boundary was noticeable on satellite, so I pulled up all of the available Day Cloud Phase RGB scales that we had, including from MesoAnywhere.

The boundary is noticeable, but what stood out to me more was the motion of the low-level clouds in the MesoAnywhere product compared to the others. It seems that the motion of the high cirrus clouds was affecting how the motion of the low cumulus was being depicted. Instead of moving to the north like in the other 3 panels, it shows a general west to east motion.

While this doesn’t matter so much in this case since we did have a meso sector available, this becomes a problem if we don’t. The CONUS imagery offers a much better picture of how the clouds are actually moving, but we lose out on the 1 minute imagery.

ei2018

SPG Blog Post Day 2

 Today, forecasters were located over the MLB and TBW CWAs for a marginal risk over the FL peninsula. Stationary frontal boundary right over the peninsula, with some sea breeze boundaries right along the coastline. Today, I was simulating a forecaster at the MLB office.

Figure 1: SZA Comparison ECONUS Product 

• Around 18Z, I noticed the SZA product had better resolution for analyzing cloud top structure, and picking out some finer details.
• The SZA and RGB product became more similar later in the afternoon, which is expected. Resolution began to improve on SZA compared to RGB closer to sunset.

Figure 2: OCTANE CTC

• The CTC product was great for identifying rapidly developing storms during this event. There was one impressive cell that developed by Kissimmee, and the CTC product highlighted these cloud tops very well.
• From a forecaster perspective, it helped me to pinpoint an area that needed further analysis, and my team and I decided quickly afterwards that a warning needed to be issued for this storm.
• The speed product was also helpful for visualizing storm motion. Rescaling the product back out to the CONUS scale helped put into perspective where faster moving storms were located.
• Additionally for the OCTANE suite, I paired the MesoAnywhere, LightningCast spotlight, and MRMS data in a perspective. In this perspective, I had the “red” 0-10 minute values flashing, and semi-transparent, so you could see the data below the stoplight.
• Stoplight was very helpful in the DSS realm. I used it for a quick guide to respond to partners about event precautions.

Figure 3: WV/WVT/IRob/VISob Compare 4 panel

• Something very interesting that was noticed on the WVT imagery, was sea breeze moisture moving in on the FL east coast. I toggled with the colormap a little bit, making the minimum be 0.2, and the maximum be 1. This makes it a little easier to watch the darker colors, representing the moisture, move in from the ocean. Very interesting feature to capture on the simulated satellite imagery!
• The 5.15 imagery did not seem to capture this as well, which makes sense as the sea breeze was probably a very shallow feature.

Kelvin-Helm

SPG Blog Post Day 2 - Daytona RFD

 Deep convection was prevalent during the afternoon of Tuesday May 12th, 2026. There were several interesting artifacts in the satellite imagery that were noted this day. There were also several different storm types observed such as single cell “pop up” storms, a linear area of storms as well as a few supercells which eventually transitioned into clusters of slow moving storms. Something I thought was particularly unique was the Rear-Flank Downdraft (RFD) on a supercell moving north to south near Daytona Beach while there was a clear west to east steering flow.

This storm initially developed north of the area near Clay County. As it moved off the coast, it strengthened quickly then had an anomalous southerly storm motion as everything else was generally moving east. As the storm pulsed up and down in strength, there were periods where the OCTANE Speed imagery caught the RFD pop out with the green coloring west of the main updraft. You can see that below on Figure 1.

While this is not something out of the ordinary, it was most visible on this satellite product because upper level cirrus blocked this process on other satellite imagery.  

Figure 1: Rear-Flank Downdraft (RFD) captured on the Octane Speed imagery as a storm with anomalous south motion moves through the easterly flow.

DSS: Max Road Fire

 During Day 2 of the Hazardous Weather Testbed, we provided mock-DSS to the Max Road Fire located in South FL along the Broward and Miami-Dade county line. Since this was a DSS event, we evaluated the two most important products related to lightning onset and cessation, LightningCast V1 vs V2 and the Stoplight product, at the fire location making sure firefighters had ample lead to time to seek shelter before lightning struck the area. We also requested an on-demand dashboard display of LightningCast V1 and V2 at the exact fire location to help monitor probability trends of lightning activity.

Figure 1 (above): shows an animation of LightningCast V1 (images on the left) vs Lightning V2 (images of the right). Notice the higher probabilities indicated by V2 on the right of up to 70% vs  50% on the left. It turned out that LC V2 provided a much longer lead time of lightning onset just outside the range ring over the fire location.

Figure 2 (above): shows the Spotlight V2 product (GLM FED + ENTLN combined) confirming lightning activity at 1921Z outside of the 8-mile radius from the fire location.

Figure 3 (above): shows a time series plot showing the probability trends of lightning at the exact location of the fire and also the maximum probability of lightning within the 8-mile radius of the fire location. Lightning was detected by the GLM instrument around 2041Z (image below) when the LightningCast probability trends showed a rapid upward trend in probabilities (image above)

Lastly, the Solar Zenith Angle imagery below provided a clearer view of the texture of the clouds right on the coast just north of Miami roughly an hour before sunset when compared to the traditional imagery on the right.

Figure 1: Solar Zenith Angle imagery at 606 PM EDT, almost two hours before sunset. Sunset at Miami (MIA) was at 7: 58 PM as shown on the Climate Daily Report (CLI) from NWS MFL.

Hurricane Specialist

Overview: Week 2, Day 2

10 AM

Tuesday began with a group discussion and first impressions for the five experimental products. Topics included how forecasters applied LightningCast and the Lightning Stoplight, OCTANE Cloud-Top Cooling for monitoring updraft strength, and the value of SZA imagery near sunrise to observe low clouds and fog. I showed an example of the SZA Day Cloud Phase Distinction RGB on CIRA-SLIDER, with clouds and storms across Florida around sunrise. I asked the forecasters to identify what time the imagery became 'usable' for them, and compared it against the traditional imagery of the same scene. Here were the results:

• Traditional imagery:
• SZA imagery:

I'm hoping to run a similar experiment with SZA imagery near sunset tomorrow. Here's the imagery I showed today. When do you think each imagery becomes 'usable'?

Traditional Day Cloud Phase Distinction RGB

SZA Day Cloud Phase Distinction RGB

We jumped into our forecast discussion, which asked the question 'Can we avoid going back to Florida again?' Unfortunately that answer was NO, so we localized to NWS Melbourne, FL and NWS Miami, FL.

1 PM

Shortly after ops started SPC issued an MD for the Florida peninsula.

Forecasters in the MFL office talked about providing DSS with LightningCast and Lightning Stoplight, and noticed in the OCTANE MesoAnywhere product how cirrus motions aloft cloud interfere with low cloud motions. MesoAnywhere is on the left, ABI MESO imagery is on the right.

Forecasters in the MLB office issued a handful of warnings, and we had a discussion about the OCTANE-CONUS Cloud-Top Cooling product. While the OCTANE MESO products showed more information, forecasters still found the OCTANE-CONUS products useful if a MESO wasn't availalble in this case.

Late in the day we viewed the frontal boundary in KS where storms might initiate this evening through the Synthetic GXI products, namely the 5.15 µm and WVT products. We compared them with the ABI split window moisture field (10.3-12.2 bands) and the ALPW from JPSS. In talking with another developer, we got the idea to create a 'sandwich' product that meshes the WVT and ABI Split Window products.

-Kevin

Monitoring LC V1 and V2 in Florida

At the beginning of week #2, forecasters were over Florida getting used to the products that they would be looking at for the week. For the Lightningcast product, one of the questions that was being asked by developers was differences between Version 1 (V1) and Version 2 (V2). V1 included 4 ABI inputs (channel 2 [the red band], channel 5 [the snow/ice band], channel 13 [the IR-window], and channel 15 [the dirty IR-window]), with V2 also including Muli-Radar Multi-Sensor (MRMS) reflectivity at -10C. Contours for both versions are shown in figure 1. Both versions looked fairly similar in the spatial extent and timing of the contours.

Figure 1: Lightningcast contours for V1 (left panel) and V2 (right panel) over Florida on 11 May 2026 from 2026Z to 2121Z. Satellite imagery in the background is the Day Cloud Phase Distinction RGB from GOES-19.

While not examined by forecasters today (but will be for fictional DSS events later in the week), the lightning dashboard for the Gainesville Regional Airport (KGNV) showed that V2 had a better handle on lightning cessation than V1 for that particular location (figure 2). V2 showed a ~5% probability of lightning within the next hour at 2050 UTC, while V1 reached that same probability at 2118 UTC, roughly 30 minutes later.

Figure 2: Lightning dashboard for KGNV. V1 probabilities at that location are shown by the red line and V2 probabilities at that location are shown by the green line. The GLM flash counts within 5-miles/5-min (8-miles/5-min) are shown by the dark (light) blue circles.

-Aurora

GXI 0.91 µm-based WVT Imagery of a Florida Sea Breeze

Figure 1: GeoXO/GXI water vapor transmittance (WVT).  At 20 UTC (last frame), the subtle darker shading near the coast shows the extent to which the sea breeze has moved inland.

Figure 2: Associated 20 UTC dewpoint from HRRR. Image from pivotalweather.com.

Today’s operations focused on convection moving across Florida with an associated sea breeze on the eastern coast. This provided an opportunity to see how this feature might appear in future GeoXO GXI imagery.  We looked at synthetic GXI imagery based on the 00 UTC HRRR output from the same day.

Figure 1 shows a short loop of synthetic water vapor transmittance (WVT) imagery.  WVT is the reflectance ratio of the 0.91 to 0.86 µm channels, and oftentimes better highlights areas of moisture than the 0.91 µm channel alone.  Darker areas (i.e. lower values) of WVT generally represent areas with higher total column water vapor.

At the end of the loop, as the sea breeze establishes itself inland (as demonstrated by the forecast dewpoints in Figure 2), a subtle area of darker shading in WVT is visible near the coast, delineating the extent to which the sea breeze has moved inland.

The dewpoint gradient across the sea breeze is only a few °F, which explains the subtleness of this feature.  Stronger sea breezes with larger moisture gradients will be much easier to identify than what is seen in this example (as regularly demonstrated in WVT from EUMETSAT’s Flexible Combined Imager (FCI) over Europe).  It is also noteworthy that the synthetic 5.15 µm did not identify the sea breeze, mostly due to the limited vertical extent of the sea breeze circulation.  WVT, by contrast, is sensitive to water vapor anywhere in the column.

-VortexTilting

 

Monitoring Downburst Potential with Sea-breeze Convective Storms in Florida

In accordance with Mesoscale Discussion #705 issued by NWS/Storm Prediction Center at 1724 UTC, the main area of focus for thunderstorm downburst wind generation was set as the Atlantic coastal region of Florida from south of Jacksonville to Palm Beach County.

The initial analysis highlights a primary area of concern for severe downburst winds situated along the east-central Florida coast. This region is characterized by strong ambient instability, creating a highly favorable thermodynamic environment for robust convective updrafts. Furthermore, the convergence of lingering thunderstorm outflow boundaries with the advancing Atlantic sea-breeze front serves as a potent mesoscale lifting mechanism. This boundary interaction is anticipated to force explosive convective initiation, setting the stage for intense downward momentum transport as heavy precipitation cores develop and rapidly descend.

Figure 1: Composite of SZA day cloud convection, LightningCast lightning probability, and MRMS radar reflectivity at 1906 UTC 11 May 2026

To assess the vertical thermodynamic structure within this concern area, we examine NOAA-21 NUCAPS (NOAA Unique Combined Atmospheric Processing System) sounding profiles. These satellite-derived soundings exhibit a classic "hourglass" profile, featuring dry sub-cloud and mid-tropospheric layers flanking a moist low-level convective layer. This signature is strongly indicative of sufficient potential instability and rapid evaporative cooling. Driven by this thermodynamic structure, the NUCAPS profiles suggest a large downburst wind gust potential in the vicinity of 50 knots, placing the environment right at the threshold for severe convective wind generation.

Figure 2. Comparison of NOAA-21 NUCAPS sounding profiles in the Cape Canaveral area during the afternoon of 11 May 2026.

Corroborating the polar-orbiting data, a GOES-19 derived sounding at 1740 UTC shows excellent agreement with the NUCAPS profiles. The high-temporal-resolution geostationary sounding captures the same inverted-V, dry-adiabatic lower troposphere. Complementing the sounding data, the corresponding GOES-19 Brightness Temperature Difference (BTD) microburst risk product highlights the Cape Canaveral area as a localized maximum for severe downdrafts. The BTD product calculates a Wind Gust Potential (WGP) of 40 to 50 knots, tightly aligning with the NUCAPS assessment and emphasizing the imminent threat to the Space Coast.

Figure 3. GOES-19 sounding profile near Titusville, FL at 1740 UTC compared to an eastern U.S. sector IR BTD product image during the afternoon of 11 May 2026.

To validate the satellite-derived observations against high-resolution numerical weather prediction, we evaluate the 1800 UTC Rapid Refresh (RAP) model sounding at Cape Canaveral. The RAP model profile definitively confirms the thermodynamic signatures identified in both the NUCAPS and GOES soundings. It displays significant Convective Available Potential Energy (CAPE) coupled with substantial mid-level dry air, yielding a high computed Wind Gust Potential (WGP). This strong consensus across multiple platforms—polar satellite, geostationary satellite, and mesoscale modeling—renders a clear and consistent picture of an environment primed for significant downburst activity.

 

Figure 4.RAP model analysis sounding profile retrieved over Cape Canaveral, FL at 1800 UTC 11 May 2026.

-StormRangerWX