By WeatherFlow meteorologist Shea Gibson.
Ever wonder how a meteorologist might study the Atlantic Basin for tropical activity? Well in this article we hope to show you some great tools to use so that you may find your own bearings on how to do perform your own “tropics watch”. There are many, many products, apps and tools out there to use, so we are not giving all of them here…but just a few things we may use to make educated evaluations on what is going on in the tropics and what may happen given the data and empirical evidence we gather.
When we study the tropics, one of the first things to think about is getting a general perspective of the entire basin, which includes the North Atlantic Ocean(north of the equator), the Caribbean Sea and the entire Gulf of Mexico. It’s good to see everything in motion to view any potential areas of rotation. As you should remember, Low pressure in the Northern Hemisphere spins counter-clockwise. Conversely, High pressure spins clockwise.
So here is one way we can see everything at once with the Atlantic wide view found here the NOAA “GOES” (Geostationary Operational Environmental Satellite) site to find some useful information:
You’ll need to choose which media outlet you prefer (flash player, java, HTML5, gif’s) to use or what works for you, but there are some additional features within the flashplayer and HTML5 on each product in the list. Remember the visible satellites become infrared when darkness sets in. You can see the sunset edging on the eastern side of this map over the Cape Verde Islands off the African Coast. You can also find other smaller regions to choose from for up close looks at those areas.
Here is the “Water Vapor” imagery with the Tropical Forecast Points (track of storm) for named storms and HDW -High (upper level winds) activated. Just a way to see the path and the possible shearing factor for areas of disturbance or tropical cyclones.
The next tool that is naturally useful for us at WeatherFlow…is the map in Wind Alert to see if we can get any readings from sensors at or near areas of interest (includes ocean buoys, near-shore buoys, coastal stations and all sensors in the public domain). The other products/applications such as SailFlow, FishWeather, iKitesurf, iWindsurf and the professional product Datascope also have the 50,000+ stations available to check worldwide.
From here, you can go to the National Hurricane Center website to check for any areas of disturbance they have. This can be done first in the order, but if you really want to test yourself… you can study those Tropical Atlantic maps and the other tools below to see if there are any areas you can point out first… and then do this part lastly.
They can provide you with areas of interest – sometimes knows as “Invests”. Some of these areas are given a percentage for chance of development in the next 48hrs…and the chance of development over the next 5 days. Here we have Invest 97 (#1), Tropical Storm Danny, Invest 98 (#2), and Area of Disturbance #3 coming off the African coast.
Here is an active Atlantic Basin shot on Sunday, August 23, 2015.
Ok so now we have some information to go on as you identify “areas of interest” on your personal radar. Now we will take a peek at the SST’s (Sea Surface Temperatures) to see if water temps provide the fuel tropical systems need. There is quite a bit of variation in what constitutes ideal temperatures for tropical systems. The general idea here is that the warmer the waters are, the more favorable it is at the surface for development. There are many products out there pulling from NOAA/NASA satellites, NOAA buoys and other coastal instrumentation to find out what the SST’s are…and there are many ways to find it. Here is one I like to use – and it is fairly new from NASA…called Sport SST – and it is very user friendly.
You can choose the region to focus on and animate from past to present in 20 day increments. Makes for a pretty neat visual!
Alright so now you are on your way to being an amateur. Now we can move into the intermediate levels. Saharan Air Layer. This is where Saharan desert dust blows out over the Atlantic Ocean at the mid levels of the atmosphere and travels Westerly all the way to South America and parts of the Caribbean (even into the Bahamas and southern Florida). This is important to know if you are watching waves come off the African Coast as this dust can fluctuate light to heavy…with heavier dust events able to dry out the air so much that tropical systems cannot develop. If you are in the mood for reading more about it, I did a 3 part study about this last year 2014. Part I: http://blog.weatherflow.com/sal-ty-atlantic-the-saharan-air-layer/ , Part II: http://blog.weatherflow.com/sal-ty-atlantic-the-saharan-air-layer-part-ii/ and Part III: http://blog.weatherflow.com/sal-ty-atlantic-part-iii/
Here is a good product to use that is animated. You can see the dust levels and where it is in the atmosphere. The heavier the dust levels, the less likely a storm can develop near it. Below is Tropical Storm Danny 2015 to the far west (Invest 97 well to the north), Invest 98 behind him to the East, and Area of Disturbance #3 presently coming off the African coast.
Next we like to see what the “Precipitable Water” looks like and where the drier air is located outside of what the Saharan dust levels are showing. Along the ITCZ (Intertropical Convergence Zone), you typically see quite a bit of moisture pushing along the east to west belt of troughing, where areas of disturbance are fed into from the southwest, south and southeast. You can also see where areas of interest are wrapping moisture into the centers of these Low pressures as the animation provides a great visual. This is further evidence of possible enhancement to the system(s).
Ok so now you are becoming intermediate in what you are doing. Want to follow the rabbit hole even further? Come on let’s take a look at some advanced stuff…
This tool is the Advanced Scatterometer – or ASCAT METOP A and METOP B satellite information. This allow for vertical readings from space as Scatterometers operate by transmitting a pulse of microwave energy towards the Earth’s surface and measuring the reflected energy. The main purpose of this technology is to find out the near surface winds over the ocean. It allows for meteorologists to see what the winds are doing in these areas of disturbance…and can be attributed to naming of systems before the NOAA Hurricane Hunters fly in or buoy readings capture speeds at the surface. The satellites orbit and do what are called ascending and descending passes over the Earth. As they do, they “swath” the planet with these microwaves…which looks like ribbon strips. Within these strips are enormous amount of datasets that are very useful to meteorologists around the world.
Here is a great source from STAR (Center for Satellite Application and Research). You click on the ribbons to see the data. Wind barbs are important to know, so here is a quick wind barb chart:
Another great ASCAT source is from the Ocean and Sea Ice Satellite Application Facility. The below screenshot shows where Invest 98 is trying to develop closed Low pressure from the counter-clockwise wind barb directions.
Next up we have a fairly new tool developed by a brilliant individual named Cameron Beccario. He has created the beautiful wind mapping product http://earth.nullschool.net/ . Using this product, you look over areas for what winds are doing at most levels of the atmosphere. As things change higher up, we always have to look for upper level shear to weaken storms as cloud tops get blown off by stronger winds aloft. This limits vertical stacking and prevents tropical cyclones from developing further…and many times strips them of surface storm energy from remaining wrapped around the core.
Here is a screenshot of small Tropical Storm Danny just east of the Leeward Islands:
And here at roughly 34,000 feet (250hPa)..we see the upper level shear from the S and SW that is currently weakening him.
Ok so now you have the ASCAT information, visual satellite imagery tools (cloud types and patterns), infrared imagery, rainbow/color infrared imagery for coldness of cloud tops and shear patterns. Using this data, we may be able to deduce from what is called the Objective Dvorak Technique if you have a tropical system or not…and then put your findings to the test by going to the NHC site listed near the top of the page and seeing if they have that area circles or highlighted for observation.
You are now equipped with some good tools to use in your adventures on learning how to see what is going on in the tropics. As far as forecasting, well that may be a story for another day.
BUT, if you really want to get to an expert level, it wouldn’t hurt to look at Global patterns to see how the Hurricane Season may play out from year to year. Here are two sources to check out for a taste of what the global scientists look at:
El Niño/Southern Oscillation (ENSO) Diagnostic Discussions at:
And the Madden Julian Oscillations (MJO):
Cheers from us at WeatherFlow,
Forecast Team, SE Region/East Coast