 DISCUSSION: Recently, the internet has been abuzz with the question of whether we can blame climate change for catastrophes like Harvey and Irma.
The short answer is yes and no – and here’s why. Climate and weather are two very different things. Climate is the long-term pattern of atmospheric conditions, while weather changes day to day. Hurricanes are weather phenomena. They are caused by waves in air circulation patterns off the west coast of Africa, and gain strength travelling over warm water. So, no, climate change did not directly result in the formation of dangerous hurricanes like the ones we've seen recently. However, we can say that the effects of anthropogenic climate change made the impacts of these storms worse for two reasons: 1: Warmer air and sea surface temperatures Air/water temperature is really a measure of the energy of the molecules of the air/water. Warmer temperatures mean more molecular motion which means more energy - the energy that hurricanes feed off of. As a hurricane travels through an area of warmer air and water temperatures, its wind speeds increase. Also, because the air is warmer, it can hold more water vapor – which means more rainfall. The observed increase in both air and ocean temperatures in recent years means that conditions have become increasingly favorable for strong tropical cyclones like Harvey and Irma to form. 2: Sea Level Rise It's harder for flooding to happen if the level of the ocean starts out at a lower point. This is especially evident in cities like Miami, which already experiences a number of flood days throughout the year, regardless of whether it's a sunny day or a strong hurricane is coming through. This is due to rising sea level. With Miami flooding already from sea level rise, storm surge and rain just make it worse. This is also true for small island countries in the Caribbean that don't have the infrastructure to deal with rising sea levels. Currently, there isn't enough data to conclusively say how climate change will affect hurricane development. However, we do have enough evidence based on the basic principles of how these storms work to say that climate change will "load the dice" in favor of stronger, more severe, more dangerous hurricanes. We can also say that climate change made the storms of fall 2017 warmer and wetter than they would have been without climate change. To learn more about other tropical cyclone-related events and issues from around the world, be sure to click here! ©2018 Meteorologist Margaret Orr
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 DISCUSSION: Tropical cyclones derive their energy from evaporation from the sea surface, and warmer water allows for greater evaporation. In addition, liquid water has an enormous heat capacity, meaning it takes a lot of energy/a long time to change its temperature. Thus, sea surface temperatures (SSTs) and related phenomena (e.g., the El Nino Southern Oscillation [ENSO]) can be used in longer term forecasting of tropical cyclone activity or other types of weather.
The figure above shows the SST anomalies in the western hemisphere valid on 7 June 2018 from the NOAA Office of Satellite and Product Operations website. The blues show cooler-than-normal water, while yellows/oranges indicate above-normal temperatures. The NOAA Climate Prediction Center (CPC) indicates that conditions in the tropical Pacific are currently ENSO-neutral. If you were to draw a box across the equator in the east Pacific shown above, the combination of slightly below-normal SSTs south of the equator and slightly above-normal SSTs north of the equator, would probably combine to give near normal SSTs there, consistent with the CPC. Looking at the tropical Atlantic in an area stretching from the coast of Africa to ~60W and from ~5-20N (where the strongest tropical cyclones in the Atlantic basin tend to develop), predominantly below-normal SSTs exist. El Nino (La Nina) tends to inhibit (intensify) tropical cyclone activity in the Atlantic basin, while ENSO-neutral conditions don't provide a strong forcing for or against Atlantic tropical cyclone activity. However, the cool SSTs in the tropical Atlantic are not favorable for storm formation. Based on the discussion above, we may expect these cool Atlantic SSTs and ENSO-neutral conditions to persist for at least the next month or two. The CPC has predicted a normal to slightly above-normal tropical cyclone season in the Atlantic this season (for more information on this forecast click here). An important question to ask is whether the information above, specifically the cool Atlantic SSTs, is inconsistent with the CPC's outlook. The answer to that question is not necessarily. Many of the strongest storms tend to form in the area indicated above off the coast of Africa, but destructive storms can also develop in the Gulf of Mexico and off the eastern seaboard of the U. S. where water is currently warmer than normal. In addition, three months from now in the climatological peak of the Atlantic hurricane season, the waters may warm up in the main development region. Hence, despite the cooler waters in the tropical Atlantic today, if you live in a hurricane-prone region around the Atlantic basin, it is still important now to prepare for whatever this season brings. To learn more about other tropical cyclone related stories from around the world, be sure to click here! © 2018 Meteorologist Dr. Ken Leppert II Importance of Grasping a Tropical Cyclone's Storm Surge (credit: Meteorologist Jordan Rabinowitz)6/3/2018  DISCUSSION: As we get deeper into the 2018 tropical Atlantic hurricane season, many people living both across the United States and around the world often have many questions regarding various aspects and dangers both directly and indirectly related to tropical cyclones. Among such questions, often includes a curiosity for a what the definition of storm surge is and why it is so important to understand what a storm surge physically is. It is so important understand what a tropical cyclone’s storm surge physically is because a storm surge is typically the most destructive force tied to a landfalling tropical cyclone both across the tropical Atlantic Ocean (and often in any tropical cyclone-producing basin around the world).
A storm surge is best characterized as the above-normal rise in sea-level height both in advance, during the potential landfall of, and during the aftermath of a given tropical cyclone due to a nasty combination of both stronger regional atmosphere pressure differential and strong onshore winds. This destructive combination of factors (especially in stronger tropical cyclones with maximum sustained winds of at least 100 miles per hour or 44.7 meters per second) often will lead to an increase in the localized sea-level in the immediate vicinity of the storm. This localized increase in the average sea-level height near and within the tropical cyclone region is due to the presence of the substantially lower atmospheric pressure tied to the core of the given tropical cyclone. This notably lower minimum central pressure creates a stronger pressure gradient between the inner-most parts and the outer-most parts of the given tropical cyclone; thereby creating larger wave actions and swells. As a consequence of this large wave and swell production by a more intense tropical cyclone and a potential landfall situation characterized by a higher mean sea-level height along with anomalously larger waves/swells, this creates the infamous aspect of tropical cyclones which is observed as the tropical cyclone’s storm surge. When in the path of an intensifying tropical cyclone (and especially if you or family/friends live and/or are visiting a vulnerable coastal region), it is imperative to always communicate such tropical cyclone threats well ahead of time so there is adequate time for action. The reason for this is because in cases involving much larger tropical cyclones (i.e., in terms of their total spatial coverage in terms of square miles and total diameter from side-to-side), such as Hurricane Katrina (2005) or Hurricane Ike (2008), a substantial storm surge began impacting many coastal towns/cities well ahead of the core of each respective tropical cyclone landfall. Therefore, in these such cases, waiting until there was a sense of greater reactive urgency made it too late for any action to do any real good. Thus, it is always critical to respect the natural power of tropical cyclones the natural imposing threat created by an increasing storm surge both prior to, during, and sometimes even after landfall due to the wrap-around the tropical cyclone’s wind field. To learn more about other tropical cyclone related stories from around the world, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz |
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