Hurricane Season in the Atlantic: Invest Area 99L and TS Gaston

Ahh…it is that time of year again, it’s hurricane season for the Atlantic and Pacific Oceans; the blog will focus on the Atlantic hurricane activity that is ongoing. Two to mention that are active right now are the Invest Area 99L and Tropical Storm Gaston. The current status of both Invest Area/Tropical Storm whereabouts can be seen via the National Hurricane Center website.

Monitoring severe tropical weather events from the range of invest areas, tropical depressions, tropical storms to the order of Category 1-5 hurricanes by National Weather Service (NWS) forecasters can be challenging. Whether if the tropical event is occurring during the day or night, NWS forecasters can utilize satellite products and supplemental products to provide the best forecasts for the general public. One of the big challenges for forecasters is monitoring these events during the night-time. A product to consider is the Near-Constant Contrast (NCC), derived from the Day-Night Band (DNB), a sensor on the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on-board the Suomi-National Polar-orbiting Partnership (Suomi-NPP) satellite. The NCC has the capability of observing night-time light emissions and atmospheric features across the globe, including monitoring tropical storms.

The following animated gifs below highlight the NCC with infrared (IR) satellite imagery in the early morning near 5Z and 6Z, 26 August, 2016 of Invest Area 99L (Figure 1) and Tropical Storm Gaston (Figure 2), respectively.

Invest Area 99L


Figure 1: The Invest Area 99L is currently hovered over Hispaniola in the Caribbean Sea (white circle) and has a 30% chance of formation in the next 48 hours. Within the animation, NCC is shown first depicting the distinct cloud cover of the invest area, and IR shown second showing the brightness temperatures (in degrees Celsius) of the cloud convective tops. If you look closely you can see lightning (horizontal white streaks) embedded in the storm. Cloud cover and city lights are depicted as well.

Tropical Storm Gaston


Figure 2: Tropical Storm Gaston located in the mid-Atlantic Ocean has a chance of becoming a Category One Hurricane within the next 48 hours as well. Within the animation, NCC is shown first depicting the circulation of the tropical storm in the Atlantic, and IR shown second highlighting the brightness temperatures (in degrees Celsius) of the cloud convective tops. Lighting are also seen embedded in the storm while cloud cover and city lights are depicted as well.

Additionally, here are the variety of forecast track model outputs for Invest Area 99L and Tropical Storm Gaston for the next few days.

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VIIRS Flood Detection Product: Gulf Coast Flooding, August 2016

The Gulf Coast has taken a major hit lately with intense rainfall and flooding across the area (Figure 1, below). This past weekend (12 August 2016 through today) there has been a Federal Flood emergency declared in the state of Louisiana. The areas that has been hit the most is south-central and southeastern Louisiana. A summary of the flooding with images across the state can be seen through the link here.


Figure 1: Two people stranded in high flood waters in Louisiana over the past weekend (Source: The Weather Channel).

From the lower mississippi River Forecast Center (RFC), Figure 2 highlights the observed precipitation (cumulative) for the last five days (not including today) along the Gulf Coast states.


Figure 2: The observed precipitation for the state of Louisiana for the last five days. One can see the south-central and southeastern parts of Louisiana have been tremendously inundated with these areas having more than 20 inches of rainfall in the short time span. 

Interestingly enough, observed precipitation from events such as the one mentioned above can be compared to satellite observations. This comparison can be shown through the animated GIF below that changes from the Google Map view of south-central and southeastern Louisiana to the Visible Infrared Imaging Radiometer Suite (VIIRS) Flood Detection Product. The date of the images is for 15 August 2016 at 1930 UTC. Make sure to click the image for animation to occur.


If we take a closer look at the VIIRS Flood Detection Product (Figure 3) we first look at the legend for interpretation. The product shows the ‘floodwater fraction percentage’ from 0-100% for each pixel, where the spatial resolution is at 375 meters. In addition to the floodwater fraction percentage, are the scene types that can be present in each pixel. Scene types range from land (LD, light brown), Supra-snow/ice water (SI, magenta), snow (SN, white), ice (IC, aqua), clouds (CL, light grey), cloud shadow (CS, dark grey), and open water (WA, dark blue). From the legend and images, one can see and discern the areas of Louisiana that experienced the most flooding which coincide with observed precipitation measurements.


Figure 3: The VIIRS Flood Detection Product highlighting the areas of Louisiana that experienced the most flooding. The legend and interpretation of the color scheme is shown above.  

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