A Normal Start to the 2019 Tropical Storm Season

Two years ago this week Texas and the Gulf Coast were dealing with Harvey, which waddled over the southeast Texas and Louisiana coasts for three days after making landfall, dumping record amounts of rain. Harvey was the eighth named tropical cyclone of the 2017 season. Here in 2019 Tropical Storm Dorian is the fourth named storm of the season, and the former Tropical Depression #6, located midway between the U.S coast and Bermuda, became Tropical Storm Erin Tuesday evening. Right now 2019 is mirroring last year with one named storm in June (Andrea), two in July (Barry, Chantal), and two in August.
 

Atlantic tropical cyclones as of 10:50 p.m. EDT August 27, 2019. Source: National Hurricane Center

The 2018 hurricane season finished strong, with a total of 16 named storms ending with Hurricane Oscar at the end of October. Four of those storms made landfall in the U.S. Hurricane Michael was a Category 5 hurricane when it made landfall on the Florida Panhandle on October 10.

Track map of all 2018 tropical cylones.

A "normal" tropical storm season (June 1 - November 30), based on data from 1966-2009, is 11 named storms, six of which are hurricanes, with two of those hurricanes Category 3 or greater.

The season tends to ramp up quickly during August and early September, with the peak about September 10.

NOAA's prediction for the tropical storm season (updated 8/8/2019), calls for a likely (70 percent confidence) range of 10 to 17 named storms (winds of 39 mph or higher), of which 5 to 9 could become hurricanes (winds of 74 mph or higher), including 2 to 4 major hurricanes (category 3, 4 or 5) (winds of 111 mph or higher).

All eyes are now on Tropical Storm Dorian, located tonight just east of the Leeward Island and headed toward Puerto Rico. Dorian has not changed much in intensity as of this writing, but is expected to strengthen some before moving across Puerto Rico. The higher terrain of Puerto Rico will cause it to lose some intensity tomorrow before it again emerges over open water and strengthen again late this week. Based in current forecasts Dorian could be approaching Florida by late this weekend. There is a higher than normal uncertainty of the intensity forecast of Dorian due to a large spread in storm model guidance.

"Strengthening" and "weakening" can be somewhat misleading descriptions with tropical systems like this. While winds are what most people tend to think about and focus on, the storm surge, heavy rain, and resultant flooding are what often cause the greatest threats to life and property. You don't need a particularly intense system to produce a lot of rain.

Dorian bears watching. Erin, on the other hand is expected to turn northeast into the Atlantic and weaken to a tropical depression in the next three days. You can find the latest information on Dorian and other tropical systems on the NOAA/NWS National Hurricane Center web site.

The Latest NWS Forecast on Your Smartphone

It looks like an app, it sort of acts like an app, but it's not an app. If you are interested in the latest forecast, advisories, warnings and watches, then a link to the National Weather Service "mobile web" is something you should have on your smart phone. There are literally hundreds of weather apps of one kind or the other, and as usual with something like apps they run the range from just plain bad to very useful. Most of the forecast apps simply run algorithms to display model output data for a day or location, and there is little or no human input. This is my go-to "app" for weather info on my phone.

When you open NWS Mobile Weather, you have a well-organized display that shows the current conditions, the forecast, and other information for your chosen location.

The opening screen for NWS Mobile Weather (left), and the second half of the page seen by scrolling down (right).

In addition to the graphical forecast on the opening page, you can select Detailed Forecast which provides the complete 7-day forecast for the location selected.

The one feature I really like with this is that you can save multiple locations to a list. If you have regular (or non-regular) places you visit you can add them to the list. Tap on the location field and a drop down list of all of your locations is displayed. Select the one you want, and the latest forecast and other data will be displayed for that location. You can also edit this list, deleting locations you no longer want, or change the name of the location to something more descriptive to you, for example "Uncle Bob" instead of "Springfield, (pick your state)".

To install this link on your smartphone follow the instructions found at https://www.weather.gov/wrn/mobile-phone. The instructions differ slightly between iOS and Android phones, but in either case it's just three steps.

As I was putting the finishing touches on this post today I came across a Forbes article written today by Dr. Marshall Shepherd, Director of the University of Georgia’s (UGA) Atmospheric Sciences Program, titled "Why Doesn't The National Weather Service Have A Weather App?"  This provides some explanation why the NWS doesn't have a full-blown app and instead developed this mobile web link. In the article he mentions an app called NWSNow that lists some very nice features, but it appears to be no longer available.

After a Soggy Spring and Early Summer, Drought May be Creeping Back

After a wet spring and early summer in much of the central and eastern U.S., dryness has become more established in the past three weeks especially in the central U.S. At the same time, drought conditions in the southeast U.S. have diminished in the past two months.

The maps of percent of normal precipitation for the U.S. the sharp contrast in precipitation between the period of May 1 through June 25, and from June 26 through the end of July.

The U.S. Drought Monitor released today is showing some expansion of D0 (Abnormal Dryness) across the central U.S. compared to a month ago, especially across the corn and soybean belt. Corn and soybean planting was delayed several weeks in some areas because of heavy rain and the resulting saturated ground and flooding. The dryness is spreading just as the corn is starting to pollinate in many areas, about two to three weeks later than normal.

The U.S. Drought Monitor for July 30 (l) and June 25 (r)

The rapid transition from wet to dry conditions is dramatically seen in the CoCoRaHS Condition Monitoring Report maps especially in the Midwest. The first map below is the condition map as of today, and the second map shows the conditions as of June 24. Note the moderate to severely wet conditions from Iowa through Illinois, parts of Missouri, and into Ohio as of June 24. In five weeks most of those have changed to normal to moderately dry.

CoCoRaHS Condition Monitoring report maps for the week ending August 1 (top) and ending the week of June 24 (bottom)

This may be the makings of a flash drought from Iowa though central Illinois into Ohio, as well as Michigan. A flash drought is characterized by a relatively short period of warmer temperatures and rapidly decreasing soil moisture. The "flash" refers to the rapid onset of drought, not the duration. In parts of the Midwest almost a month's worth of rain fell in the first week of July, but little since then. The last three weeks of the month were also extremely warm with highs in the 90s and 100s. At the same time, rain became scarce.

For example, at my location in east-central Illinois, I received more than 4 inches of rain the first week of July, close to normal for the entire month. During the last 24 days of the month I received only 0.22 inch. The ground went from being saturated to rock hard with cracks forming by the end of the month.

This is where CoCoRaHS condition monitoring reports can be very helpful. While July precipitation was near normal in my case, it doesn't tell the whole story because the rain largely occurred in a few days. Condition monitoring reports submitted weekly help those monitoring drought and environmental conditions to discern the current state and the impacts of too much or not enough precipitation.

Hail Season is Here

CoCoRaHS' annual Hail Week is coming to a close and will end with "Put out Your Hail Pad Weekend" this weekend. If you have been following this week's Messages of the Day you have seen how to measure hail, report it, and how to make a hail pad. (Mobile app users should select "View message of the day" after submitting you daily observation.) Hail is a fascinating phenomena and there is a lot of information available if you want to learn more about it. The CoCoRaHS Hail page  has some information, and you can find a lot more information at Living With Weather- Hail on the Midwestern Regional Climate Center website.

Compared to the past few years this season is getting off to a slow start in the hail department. Depending on how the rest of April goes the number of national hail reports for the first four months of the year should be about the same as last year, but well below the previous three years.

Hail reports for January through April for this year and the past four years

Normally probabilities for significant hail very low at the end of February and only begin to ramp up in mid-March to early April. Here are the climatological probabilities for significant hail from the the NOAA Storm Prediction Center for mid-April, late May, and August. The center of the high probabilities moves north through April and May, reaching a peak in late May. By early August probabilities are diminished and continue to diminish into early fall.

So far CoCoRaHS observers have submitted hail reports on 72 of 109 days so far this year, about the same as last year.This map is a compilation of hail reports for the year through April 16 from the Storm Prediction Center.

CoCoRaHS has one of the most comprehensive collections of detailed data on hail. While measuring and reporting hail may seem to be secondary to rain and snow, our hail observations provide valuable information not only to the National Weather Service but to others such as the insurance industry. A recent article in the Washington Post noted that Texas has experienced 36 $100 million disasters from severe thunderstorms in the past 25 years. Twenty-nine of these $100 million disasters were from hail!

Measuring hail is a core mission of CoCoRaHS, and the separate hail reports on the CoCoRaHS web site allow you to submit your hail information. There are a few things you need to know before measuring hail, and you can find that information in our "Measuring Hail" training animation. Here is a hail size reference and measuring guide you can download, print, and laminate for use. The rule on the bottom is to scale and fits on a 3x5 card. Make multiple copies and keep one at home, in the car, or at work.

The March of the Seasons – Precipitation and Temperature

CoCoRaHS is all about measuring precipitation locally, and contributing to the "big picture" of precipitation across your state and across the country. We get a good idea of how precipitation varies on a daily basis by viewing our observations and those of other CoCoRaHS observers, but it's a little more difficult to get your head around how precipitation varies each day, on average, across the country.

Climatologist Brian Brettschneider is big on maps. He recently compiled an animation of average daily precipitation across all 50 states using PRISM data for the period 1981-2010. He used gridded precipitation data at a resolution of 800 meters. These are the same data that are used to generate precipitation normals for each CoCoRaHS station. The animation is composed of plots of average daily precipitation for each day of the year.

It’s fascinating to watch the expansion north and west of daily average precipitation values in the central U.S. beginning in late January and peaking in early June. The Continental Divide is clearly delineated by the pattern of average daily precipitation values in early June. Low average daily precipitation values start to expand in southwestern Arizona and southern California beginning in late March and early April and continuing to expand north through California through July. The Southwestern Monsoon is evident beginning in late June through early September in Arizona, New Mexico, and western Texas. You can see the effect of Pacific storms in Washington, Oregon, and California in the winter months, and the increase in precipitation along the Gulf coast and Florida during the summer. If you rerun the animation several times and focus on different parts of the map you will notice a number of other interesting features.

Every CoCoRaHS observer can access their PRISM monthly precipitation data through the My Account option on the top line menu after logging in. You can learn more about the CoCoRaHS PRISM Portal on the CoCoRaHS web site.

In addition to the precipitation map Brian compiled a similar map animation showing the daily average temperature through the year.

You can follow Brian Brettschneider on Twitter (@climatologist49) to see some of the fascinating maps he produces. He also has a Facebook page, Alaska Climate Info.