Today, June 1st is the start of the Atlantic Basin Hurricane season…so now is the time to prepare for this year’s tropical season. To assist with your planning process, we have evaluated the NOAA 2017 Atlantic Basin Hurricane Outlook which was issued on May 25th, 2017 as well as the Colorado State University Outlook updated today. In this post, we will highlight some insights on what we could see this tropical season. Even if you do not live along the coast, we encourage you to monitor tropical activity as any tropical connection can increase the risk of flooding.
NOAA 2017 Atlantic Hurricane Outlooks
The NOAA outlooks indicate a near to above-normal hurricane season is most likely. The breakdown of the probabilities is a 45% chance for an above-normal season, a 35% chance for a near-normal season, and a 20% chance for a below-normal season. With this outlook, NOAA is predicting:
- 11-17 Named Storms. (Note: these numbers include Tropical Storm Arlene which formed in April. So we still have the potential for 10 – 16 storms.)
- 5-9 Hurricanes
- 2-4 Major Hurricanes
For a point of reference, the average number of tropical systems in a season based on storms from 1981-2010 is
- 12 named storms
- 6 hurricanes
- 3 major hurricanes
The Colorado State University Forecasts
Colorado State University (CSU) updated their initial April outlook on June 1st and is now calling for a near-average 2017 Hurricane Season. This is an increase of their early April predictions. The CSU team predicts:
- 14 named storms (which includes Tropical Storm Arlene)
- 6 hurricanes
- 2 major hurricane strength
For more information about the Colorado State University Outlook, see their Press Release.
What are the key drivers for the NOAA Outlooks compared to the CSU Outlooks?
According to the NOAA outlooks, they focused on three elements through the period of August through October as the main drivers of the 2017 Atlantic hurricane season outlook. These factors include:
- Either ENSO-neutral or weak El Niño conditions are expected over the tropical Pacific Ocean (ENSO refers to El Niño/ Southern Oscillation, which has three phases: El Niño, Neutral, and La Niña.),
- Near-or above-average sea-surface temperatures (SSTs) across much of the Atlantic hurricane Main Development Region (MDR), which includes the tropical North Atlantic Ocean and Caribbean Sea between 9.5°N and 21.5°N latitude), and
- Near-average or weaker-than-average vertical wind shear in the MDR.
(Note: Wind shear or stronger winds that shift in direction and speed as you move vertically in the atmosphere tend to break apart tropical systems. Hurricanes prefer areas of weaker shear as those more favorable conditions allow the storm to draw upon warm ocean waters and foster storm development.)
The ENSO state is one if the key questions with this hurricane season. Neutral conditions are more favorable for hurricane development whereas El Niño conditions (where the Pacific Ocean 3-month average sea surface temperature is warmer than normal.) are a less favorable environment for Atlantic hurricanes. El Niño typically causes the upper-level winds to increase in the Caribbean and Atlantic, which in turn increase the wind shear. As mentioned earlier, wind shear prevents hurricanes from being able to organize and strengthen…thus is not favorable.
The current ENSO forecast shows that we may transition to weak El Niño conditions or remain in neutral conditions this summer. Some of the challenges, however, are the fact that ENSO models show a range of solutions. So confidence in the hurricane outlooks is somewhat lower because we do not have a clear signal if we will transition to an El Niño or remain in Neutral conditions. In addition, the ENSO models tend to be more accurate in the June to December timeframe vs. the February to May timeframe. Because the ENSO forecast was created in May, the time that the forecast was generated decreases the confidence. Another question is if we do transition to an El Niño, will it be strong enough and long enough to influence the atmospheric circulations to impact on hurricane development. For more information about the ENSO forecasts see the International Research Institute (IRI) ENSO Forecast, issued on May 18, 2017.
The NOAA outlook reinforces that in addition to the ENSO uncertainty, there is uncertainty with the sea surface temperatures in the MDR forecast region (or the main area we watch for hurricane development.).
a combination of El Niño, a cooler MDR, and near- or above-average vertical wind shear in the MDR, would likely yield levels of activity toward the lower ends of the predicted ranges.”
For more information about the drivers for the NOAA outlook, see their press release.
The Colorado State University team indicates the reason for their forecast increase was
Reduced likelihood of a moderate El Niño and recent anomalous warming in the tropical Atlantic (sea surface temperatures).
The tropical Atlantic has anomalously warmed over the past two months and is now warmer than normal. In addition to providing more fuel for tropical cyclone formation and intensification, warmer tropical Atlantic sea surface temperatures are associated with a less stable atmosphere as well as moister air, both of which enhance organized thunderstorm activity necessary for hurricane development.
What Is the Difference between a Tropical Storm and a Hurricane?
Basically, the difference in the classification of a system is related to the sustained wind speeds of the storm.
- Tropical Depression – tropical system with sustained winds of 38 mph and less
- Tropical Storm – tropical system that has sustained winds between 39 mph and 73 mph.
- Hurricane – tropical system with sustained winds of 74 mph and higher.
- Major Hurricane – tropical system that has sustained winds of 111 mph and higher. This is a Category 3, 4 or 5 storm and will lead to significant impacts, especially if the center of the storm comes ashore.
Video shows of levels of damage as wind speeds increase
Why do the Hurricane Outlooks matter?
While it does not take an above-normal hurricane season for serious damages and impacts to occur, an above normal season increases the odds that a tropical system will reach the US Coast. This is simply because we expect to have more storms in the Atlantic Basin so if you have more storms it increases the chances one will come ashore. However, it does not guarantee that we will have US landfall. Also, it only takes one storm to cause serious damage to a region, which can occur in any year, even a below normal hurricane season. So whether the forecast is for above, below or a normal hurricane season, people are urged to take proactive measures to be prepared if a Tropical Storm or Hurricane Watch or Warning is issued for your area.
Even though Atlantic Hurricane season is June 1 through November 30th, the peak of hurricane season is middle August through middle October.
Early June is a good time to take your hurricane preparations so that you can move quickly if one is forecast to impact your area. In addition to having a disaster readiness kit, to shelter in place, you need to be prepared to evacuate. While we recently provided a blog post that offers ideas of “What to include in a Disaster Readiness Kit.” However, if you have to evacuate there are some other considerations. FIRST, you need an evacuation plan. Identify what you can quickly grab that will support you being away for several days, determine a place that is far enough inland that is safe from the wind damage of a hurricane as well as potential inland flooding. One option is to stay with friends or family. When you evacuate, take copies of insurance policies and other important documents. SECOND, now is a good time to check your insurance policy to ensure you have adequate coverage for you home, business and personal property. In addition, consider purchasing flood insurance. Storm surge and inland/freshwater flooding can cause significant damages. Flood-related damages are not covered by a standard home or renter’s insurance policy. If you have flood insurance make sure it also covers your personal property and not simply your structure. If you rent, you can take out a flood insurance policy for your personal property. Finally, given our coastal population, you may be told to evacuate several days before the storm will hit. So be prepared to be gone for several days.
The team at WxIntegrations will continue to provide relevant information and resources to help you better understand and prepare by incorporating weather impacts into your planning and response.
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