Hurricane Irma Sept 10 1100 AST

Hurricane Irma Interesting Facts

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September 08, 2017

Where did Hurricane Irma start?
According to the first forecast provided by the National Hurricane Center, Irma became a tropical storm around 16.4N, 30.3W in the tropical North Atlantic on August 30, 2017 at 15:00 UTC. This is approximately 550 km to the west of the Cabo Verde Islands. 

What are the conditions for the development of a Category 5 hurricane?
Low wind shear and high oceanic heat content. The latter is the actual fuel of these tropical systems. For Irma, there were ideal conditions during the entire track. When the storm increased to a Category 5, it was in an area where there was a sea surface temperature at least 2.7F above the seasonal average. This likely led to the final increase in intensity before making landfall.

What is the outlook for the rest of 2017 hurricane season through Nov. 30?
In 2017, we expected to see approximately 12 named storms and 6 hurricanes. So far, we have had 11 named storms and 6 hurricanes. This means we have had an above-normal season.

How do hurricanes gather strength?
The "goal" for tropical hurricanes is to extract heat and energy from the oceans — releasing this heat back into the atmosphere. This happens using evaporation from the sea surface, convection and condensation in the atmosphere, as well as an extreme increase in kinetic energy, aka wind.

What key factors affect the storm track?
Upper level conditions in the atmosphere. The ambient steering winds in the mid and upper parts of the troposphere are what direct the track of the storm.

How does historical data help predict paths, if at all?
Historical data is of limited use because the ambient atmospheric state (placement and strengths of upper level ridges and troughs) that direct the track is constantly changing, and is by definition never exactly the same from storm to storm. Moreover, the oceanic heat content and the wind shear in the atmosphere are always changing.

What is the importance of using three global weather models?
Very! At StormGeo we use the American model, the Canadian model and the European model. The track and intensity of the storm is usually more uncertain the farther ahead you forecast. By gathering and analyzing several sources with the best available model data, you will get a much better assessment of the potential risks and areas affected.

How is StormGeo using satellite data?
We use satellite data to monitor tropical storms and use the satellite output to assess model quality (position and strength of the storm, and whether this is correctly diagnosed by models).

How do weather events abroad affect weather in the U.S.? (i.e. cold weather in Siberia)
El Nino is the feature that has the most notable effects on weather in the U.S.
Technically, El Nino is the warm part of the oscillation in sea surface temperatures along the equator in the East Pacific. The effects are strongest in the winter after the onset of the event and includes cooler and wetter weather across the Southern U.S., warm weather in Southern Alaska, dry in the Pacific Northwest and wet weather across Southern California. (Source)

Can hurricanes affect the weather in Europe?
Not likely, but in theory they could. The chance for that to happen is picked up by the longer-range models. In the end, these remnants may send heavy rainfall across Scandinavia or into the continent.

What is storm surge?
Storm surge is a dramatic push of sea water inland across coastal locations in relation to tropical cyclones such as hurricanes. A broad wind field circulating around the storm’s center can push massive amounts of water into the coastline. The severity of a storm's surge is affected by the storm’s intensity and wind field, as well as the shape of the coastline and the slope of the sea floor. Most injuries and deaths associated with tropical cyclones are related to storm surge.

Note: Because each location that might experience storm surge is different, storm surge can be very difficult to forecast with precision. Therefore, it is critical to heed the directions for preparation and/or evacuation from local officials.