• Hurricane Irma Sept 10 1100 AST

Hurricane Irma Interesting Facts

1. Where did Hurricane Irma start?
It became a tropical storm around 16.4N, 30.3W in the tropical N-Atlantic at August 30th 1500UTC. This is approx. 550km to the west of Cabo Verde Islands. This is all according to the first forecast discussion provided by National Hurricane Center.

2. What were the conditions for the development of a Cat 5 hurricane?
Low wind shear, high oceanic heat content. The latter is the actual fuel of these tropical systems. For Irma, there were ideal conditions all the way. When it increased to a Cat5 it was in an area where there was sea surface temperature of at least 2.7F above the seasonal average. This could have led to the final increase in intensity into a Cat5.

3. What is the outlook for the rest of hurricane season through Nov. 30?
The average is for approx. 12 named storms and 6 hurricanes yearly. This far we have had 11 named storms, and 6 hurricanes. The available forecasts go and have gone for an above normal season overall.

4. How do hurricanes gather strength?
The aim of the tropical hurricanes is to extract heat and hence energy from the oceans and then releasing the heat into the atmosphere. This happens by evaporation from the sea surface, convection and consequently condensation in the atmosphere, as well as an extreme increase in kinetic energy that we know as wind.

5. 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 is what directs the track of the storm.

6. How does historical data help predict paths, if at all?
This is of limited use. The reasoning behind that is that the ambient atmospheric state (placement and strengths of upper level ridges and troughs) that direct the track is constantly changing, and is per definition never exactly equal from storm to storm. Moreover, the oceanic heat content and the wind shear in the atmosphere also changes.

7. 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 becomes usually more and more uncertain ahead in time, and gathering and analyzing all the best available model data will give a much better assessment of the potential risks and areas affected.

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

9. How do different weather events affect weather in the U.S.? (i.e. cold weather in Siberia)
El Nino is the one feature that has the most notable effects on weather in the U.S.
El Nino is the warm part of the oscillation in sea surface temperatures along the equator in the E-Pacific. Effects are strongest in the winter after onset of the event and includes cooler and wetter weather across southern USA, warmer weather in S-Alaska, drier in the Pacific Northwest and wetter weather across Southern California. (http://www.oc.nps.edu/webmodules/ENSO/NA_EN.html )

10. Will the hurricanes affect weather in Europe?
Not likely, but in general they could. The chance for that to happen is picked up by the longer-range models. In the end, these remnants may give extremely wet episodes across Scandinavia or the continent.

11. What is storm surge?

Storm Surge is often a dramatic push of sea water inland across coastal locations related to tropical cyclones such as hurricanes. A broad wind field circulating around the storm’s center can push massive amounts of water to the coastline. The severity of the storm surge is affected by the storm’s intensity and wind field, plus 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.