Weather Spectrum

Beryl makes 2

By: LPerezIII, 2:21 PM GMT on May 30, 2012

And with Beryl, the 2012 Hurricane Season is off to a busy start. The last time there were two named cyclones in the Atlantic in the month of May was 2007 (one was "extratropical"). And before that...1887. That's not a typo either. 1887. Ironically, the two May storms in 1887 were unnamed, but if they had been naming cyclones back then they would have had names. Therefore, I count that year.

Great. Two cyclones in May...that means it could be a hellish year for the tropics, right? Maybe. Looking at 2007, there were 15 named storms, 6 hurricanes, and 2 major hurricanes. Check the map below.

The two major hurricanes (rainbow tracks) in the Caribbean were Dean (landfall on the Yucatan and Mexico) and Felix (landfall in Central America). The two storms that affected the Texas coast were Humberto, a category 1 hurricane that made landfall just east of High Island, and tropical storm Erin that made landfall just north of Corpus Christi.

An average season usually sees 12 named storms, 6 hurricanes, and 3 major hurricanes. The 2007 season had just a few more named storms, an average number of hurricanes, and 2 major hurricanes. One major hurricane less than the average.

What about 1887? Thanks to shipping traffic back then, we know there were 19 storms worthy of names in 1887 - they were not naming them then. Of the 19 storms, 11 of them were hurricanes and 2 were major hurricanes. At least, as far as we know. It is doubtful that ships traversed the center of those storms back then (where the highest winds are in a hurricane) and doubtful they made it through if they did. It is quite possible that there were one or two more major hurricanes than what the records show. Without a doubt the 1887 Hurricane Season was a very busy season with 7 more named storms than normal, nearly twice the average number of hurricanes, and 2 major hurricanes. Only one of the 19 storms made landfall along the Texas coast. That was Hurricane 9 which made landfall as a category 1 Hurricane near Brownsville, TX. Please see map below showing the 1887 storms.

Now, there is one more season worth mentioning - 1969. In 1969 there were two tropical depressions in May. As you know, tropical depressions are not named until they become tropical storms. Therefore, I did not count it as a season with two named storms in May. However, out of curiosity I looked at that season just to see if the trend continued. Here is what I found...

In 1969 there were 17 named storms, 12 hurricanes, and 5 major hurricanes. Twice the average number of hurricanes and nearly twice the average number of major hurricanes in a year. Now, only 2 hurricanes hit the US that year. One was Hurricane Gerda that made landfall as a category 2 storm in Maine. But the storm that many remember and still talk about today is Hurricane Camille.

Hurricane Camille, a Category 5 storm at landfall, packed sustained winds of 190 MPH and a peak surge of 24 feet. It remains one of the strongest land falling hurricanes in the world. The true wind speed will never be known since all wind measuring equipment was destroyed before the highest speeds could be measured. The estimated wind gusts were in excess of 200 MPH. Camille made landfall near the MS/LA border, and Camille's surge caused the Mississippi river to back-up all the way to Baton Rouge, LA. The hurricane decimated the MS coast, and it remains the second most intense land falling US hurricanes with a minimum pressure of 26.84 inches (Normal pressure is 29.92 inches. The lowest recorded pressure in a tornado is 25.10 inches). In all, Camille was responsible for 249 deaths.

Here is the 1969 Storm Map

As a meteorologist and a person who lives in numbers, trends, and predictions, I look at this data and I say, "Wow. 2012 could be a very busy year." But what about El Nino? Everyone says if El Nino develops then the season will not be so bad. It is true that conditions will be less favorable over the Gulf for tropical storm formationif El Nino fully develops, which it has not, but 1969 and 2007 were both weak El Nino years. And that's when I say to myself, "We have no idea what Mother Nature will do." It could be a busy season.

Stay prepared and thanks for reading!

2012 Hurricane Season Gulf Coast Tropics Tropics Hurricane

Hurricane Season Refresher

By: LPerezIII, 2:13 AM GMT on May 24, 2012

In nine (9) days the 2012 Hurricane Season will officially begin. Of course, Tropical Storm Alberto technically kicked off the season for us when he formed off the coast of the Carolinas on May 19th, 2012. He did not last long though as wind shear got the best of him. That is a typical death among out-of-season tropical cyclones in the Atlantic. The jet stream still has a fairly big influence over the Gulf and Eastern US causing storms that attempt to form to struggle, especially those that form close to the coasts. Of the 66 tropical cyclones that have formed "off-season" (Dec 1st - May 31st) since the late 1800s, 40 of them occurred in the month of May. Most of the May storms affected areas in the Caribbean or out in the open Atlantic.

This map shows the 9 storm tracks of those that entered the Gulf of Mexico Basin (1842-2010)

Tropical Storm Alberto makes 10 over the time period of 1842 to 2012. Bottom line, tropical cyclones can occur out-of-season and the month of May is certainly one of the busiest in terms of out-of-season tropical cyclones.

The actual Hurricane Season for the Atlantic Basin, including the Caribbean and the Gulf of Mexico, begins on June 1st and ends on November 30th every year.

This chart (courtesy NOAA) shows the number of storms per 100 years from May-December.

So there's a very small peak in mid-May before falling to near zero before it ramps up again towards mid-June. The activity is pretty steady until just before August when things really begin to heat up in terms of hurricane activity. September 10th is the general peak of tropical cyclone activity. It begins to fall after that date until mid-October when there is another temporary spike - mostly due to the first few cold fronts moving offshore over very warm water and forming tropical cyclones - before falling to near zero by the end of December. Yes, like May, occasionally a cyclone will form in December. However, because the majority of tropical activity occurs from June to November it is this period of time that defines the actual "hurricane season".

Saffir-Simpson Scale

The hurricane categories of 1-5 are based on the Saffir-Simpson Hurricane Wind Scale developed by Herbert Saffir, a civil engineer, and Bob Simpson, a meteorologist, in 1971. It was introduced to the public in 1973 and has been used since to categorize hurricanes. The wind scale was created to describe the kind of damage that could be expected by each category. A block of sustained wind speed also defines the 5 categories. For example, a Category 1 Hurricane has wind speeds of 74 MPH to 95 MPH. More detail is included in the table below.

Even if you just skim the information below, please, at the very least, read the descriptions for potential damage and extent for each category.

Sustained Winds
Types of Damage Due to Hurricane Winds

Category 1

74-95 mph
64-82 kt
119-153 km/h

Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.

Category 2

96-110 mph
83-95 kt
154-177 km/h

Extremely dangerous winds will cause extensive damage: Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.

Category 3

111-129 mph
96-112 kt
178-208 km/h

Devastating damage will occur: Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.

Category 4

130-156 mph
113-136 kt
209-251 km/h

Catastrophic damage will occur: Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

Category 5

157 mph or higher
137 kt or higher
252 km/h or higher

Catastrophic damage will occur: A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

Hurricane Andrew - Dade County, FL - 1992

Hurricane Andrew was mostly a wind event vs. a storm surge event and practically leveled all of Dade County Florida in 1992. Andrew packed 150 MPH winds at landfall near Homestead, FL. The above picture is the result.

Storm Surge

Hurricane Ike - Gilchrist, TX - 2008

After Hurricane Ike in 2008, the coastal residents of the Houston/Galveston area know all-too-well what impact storm surge can have along the coast. Even though Ike was a category 2 hurricane at landfall, its surge was that of a much stronger storm; something the meteorology community had not expected until Ike was very close to landfall (almost too late). Ike and Katrina both produced storm surge that was well above what the expected surge was for their respective landfall categories. Conversely, Hurricane Charley in 2004 (Florida) produced a storm surge that was far less than what was expected.

Prior to 2009, storm surge predictions were included in the Saffir-Simpson categories, but Hurricanes Ike, Katrina, and Charley all proved storm surge predictions inaccurate resulting in the removal of all storm surge forecasts by category in 2009. Going forward the National Hurricane Center will continue to issue storm surge probabilities for each individual storm as it has since 2008, albeit more prominently. As most us know, storm surge can vary greatly by storm size, storm strength, geography of the landfall location, and more. Thus, the National Hurricane Center along with other government agencies are working to produce better storm surge predictions for the future. Unfortunately, more real-world data is needed to accomplish this task.

Tropical Storm Formation Areas

From the frequency chart above, we know that not many cyclones form in June (typically), but when they do occur the map below shows the likely areas of cyclone formation and their prevailing tracks.

The strongest June hurricane to make landfall near Houston/Galveston was hurricane Audrey in 1957. Audrey made landfall just east of the Sabine river in Cameron Parish, Louisiana. With wind speeds of 145 MPH she was a category 4 hurricane at landfall. Audrey remains the strongest June hurricane ever in the Atlantic Basin and left a death toll of 431 in its wake. Damage from Audrey exceeds $1 Billion (inflated to present day).

2012 Hurricane Names

Alberto - Beryl - Chris - Debby - Ernesto - Florence - Gordon - Helene - Isaac - Joyce - Kirk - Leslie - Michael - Nadine - Oscar - Patty - Rafael - Sandy - Tony - Valerie - William.

Some of these names look very familiar....

Until next time...thanks for reading!

2012 Hurricane Season

Sea-Breeze Fronts

By: LPerezIII, 3:43 AM GMT on May 17, 2012

A calm "Ahhhhh" as the salty gulf air hits your face. The sun shining brightly as the kids play in the waves at the beach. Life is good. That is, until about 2:00pm when clouds begin to darken to the north. Flashes of distant lighting and low rumbles of thunder fill the air. What the heck? No one said anything about rain!! Well, chances were good that they did, but you learned to ignore the mention of rain when the chances dropped to 20%. In all likelihood, however, it will not rain at the beach, but Houston will get dumped on by the bucket full. All thanks to the small-scale weather phenomenon called the "Sea-breeze Front".

A "Front" is nothing more than a separation between two different types of air mass. For example, a "Cold Front" is a boundary that separates cold air from the warmer air ahead of it. A "Warm Front" is a boundary that separates warm air from cooler air ahead of it. The front is always named by the air mass type that pushing the front along. So, a Sea-breeze Front is, well, a boundary and it definitely separates two different air masses, but nothing defines the temperature of it. All we know is that the breeze from the Gulf gives it its name. Hint: Air from the sea, in the summertime, is cooler than the air over the land. That's because water takes longer to heat than land does. So, technically, the Sea-breeze Front is actually a miniature cold front. Except, the air isn't "cold" by human comfort standards, but the breeze sure feels nicer than the stickier, more humid, air hovering over Houston. That much we know. Interestingly, it is the slight difference in temperature between the air over the city and the air over the water that gives the Sea-breeze Front its momentum and, ultimately, what causes the afternoon thunderstorms to form.

As the sun begins to heat the land, an air temperature difference is established between the cool moist air over the water and the warm, sometimes hot, drier air over the land. (Click image to make larger)

Because cooler air is more dense than warm air, it sinks, while the warmer air begins to rise. The sinking air over the water forms a "local" or small-scale high pressure and a low pressure forms over the land due to the rising air.

Now that a pressure difference is established, the air over the water acts to balance out the system and begins to "fill in" the air over the land that has risen into the atmosphere. Think of when you're taking a very hot shower. The steam is rising and if you crack the door or slightly peel back the curtain, you can feel the cooler air rushing in to fill-in the void of air in a sense. This pressure difference is what initiates the breeze we feel and begins the formation of the sea-breeze front.

Then as the moist air from the gulf is lifted up, clouds form. Usually nice puffy cumulus clouds at first, but as this process continues it can lead to some very intense summer thunderstorms with heavy rain and flash flooding.

This phenomenon does not occur everyday during the summer. There still has to be a friendly upper level environment that would promote thunderstorm formation. Take last summer for example. The summer-long high pressure put a lid on any possible thunderstorm formation along the sea-breeze. So, storms are not a guarantee with the sea-breeze front, but it is a mechanism that leads to more frequent storm activity just inland from the coast.

Florida is most susceptible to sea-breeze storms because the fronts come from both sides of the peninsula aiding convergence and upward moving air which eventually forms storms.

Can you spot the sea-breeze fronts in the image below?

Yep, they occur on both sides and move towards the center of Florida. It's those two lines of clouds. The brighter bulges along the line are storms that have formed along the sea-breeze. I love weather!!

Keep an eye out this summer. When it feels nice and sticky out, and the wind begins to pick up from the south...look out. If the clouds darker, it could turn into an ugly afternoon. 20% chance of rain huh? Yep. Everyday.

By the way, here is a shot of the rainfall totals over the last seven days. South and southwest Houston received a ton of rain!! At least the forecast was not totally wrong. Texas in general received quite a bit of much-needed rain. Thanks Mother Nature!

Have a great weekend everyone! Thanks for reading!

Gulf Coast Tropics

Houston/Galveston Rainfall Update 5-11-2012

By: LPerezIII, 2:10 PM GMT on May 11, 2012

The rainfall started when it was expected to, but ended earlier as a fast-moving squall line developed near Corpus Christi and tracked right up the coastline eventually reaching Galveston by about 2:35am. Police in Galveston reported power poles down across the Island starting in Jamaica beach to Downtown. The Galveston airport reported a max wind gust of 38 KTS or 44 MPH. That's under severe criteria by 14 mph. Nevertheless it seems there were a few microbursts along the path given the reports of downed power poles. A total of just under an inch of rain was recorded at the airport in Galveston.

South Houston also had it's fair share of nasty weather with wind gusts to near 40 MPH and rainfall of about 0.75 inches.

Picture below shows rainfall estimates for this weather event. Most of the heaviest rainfall remained offshore.

Click the link below to see a quick video of the squall line as it moved through.
5.11.12 HGX Radar.swf <--Radar loop of last nights squall line/bow echo.

Going forward today, we're not completely out of the woods as far as heavy rainfall threat, but the good news is that the squall line really zapped much of the instability out of the atmosphere and it will take some time and quite a bit of sunshine to reignite storms by this afternoon. It looks like the storms will begin very scattered in nature. Severe threat is minimized, but there will be a slight chance for damaging winds and hail with a few storms that form. The coastal areas will be under fire again and areas north of Houston can expect only a few passing thunderstorms or rain showers.

As for rainfall, the ground is soaking up last night's rainfall and as long as the rainfall rates remain below 2-2.5 inches per hour, the risk for flooding is much less than it was yesterday.

The sun will be shining for most of the day and it will be very comfortable until this afternoon when the humidity returns with daytime heating.

You can see the tale-tell comma shape to the low pressure. You can also see some new development towards north central Texas. We shall see what this will mean for us by this evening.

Mother's Day is shaping up to be a top 10 day as the weather is pushing through quicker than previously thought.
Have a great weekend!!


Heavy Rains and Potential Flooding

By: LPerezIII, 2:23 AM GMT on May 10, 2012

The image above is the Hydrometeorological Prediction Center's modeling of the total precipitation amount for the US over a 5-day period. This image is valid from yesterday evening until Monday evening. It is pretty intense-looking. Upwards of 6-8 inches of rainfall for the coastal areas of SE Texas, and then about 4-6 inches in the Houston area. Then 3 inches and below north of Houston. Depending on how fast this precipitation accumulates, places from San Antonio and the Central TX region east to the Louisiana border can expect to start seeing flood watches in place as you read this. Basically I-10 and areas south are most prone to the heaviest of rainfall from this system.

The culprit? An upper level low spinning across the southwest US/Mexico is tracking east towards Texas that is already beginning to generate showers in far west TX as of yesterday evening. Each radar site has a light greenish bluish ring around it, that's just clutter and false echoes, and the actual rain and thunderstorms are the areas of yellow and red just coming into far western TX.

Because I compose my posts the evening before, as you read this rainfall is beginning to affect central Texas, or the western portions of Central TX. By the late afternoon the rainfall will be approaching western portions of the southeast Texas area and Friday is shaping up to be a very gloomy day in southeast Texas.

Here is what the vorticity and heights look like at about 18,000 feet. I'll come back to vorticity momentarily.

See that cool-looking feature centered just south of Arizona and over western Mexico? The cool orange and yellow colors? Well that is the mid-level low pressure system that is generating all that rain that will eventually affect southeast TX on Friday. The colors denote areas of strong vorticity. What is vorticity??

Vorticity is a measure of the rotation of air in a horizontal plane. Positive vorticity (air rotating counter-clockwise or cyclonic) can be correlated with surface low development and vertical motion.

When the air spins counter-clockwise in the upper levels of the atmosphere it causes divergence or air to spread apart ahead of the rotation. Think about water for a second, if you try to spread water apart in a pool with your arms what happens? Water fills in the void from below. The same thing happens with air (they are both fluids; water & air). So when air separates far above the surface of the Earth as a product of rotating air (vorticity), air fills in from below, or from the surface. As air moves vertically, the pressure at the surface drops and a low pressure area forms.

In the image below, notice the rainfall (areas of green) is falling ahead of the vorticity areas on the prior map. Where the rain is falling is where the surface low is developing or has developed.

Knowing what we know now about vorticity and the formation of a surface low pressure and consequential rainfall we can look at the vorticity for the next few days and guess where the rain will fall.
By mid-day tomorrow, across central TX.

By Friday morning, across southeast Texas.

This is the precipitation estimates for the same time as the above image...

Note the heaviest rainfall is ahead of the upper low. This is because that is where the best upward motion is as a result of the air spreading out allowing air to rise. As unstable, moisture-filled, air rises it condenses to form clouds and when the air continues to rise quickly it builds into rainstorms and thunderstorms.

This upper level system is potent. Some severe storms are possible where the sun can shine for a bit to heat the ground which heats the air and increases instability in the lower atmosphere. If this happens, there is a small potential for a few tornadoes. However, if cloud cover hinders sunshine then it is less likely we will see tornadoes and more likely we will see some strong wind gusts from storms.

The rain will be consistent through the day on Friday and Friday night, especially along the coast before becoming a bit spotty in nature early morning on Saturday through mid-day. Scattered showers will be possible for the remainder of the weekend and you might have an umbrella handy for Mother's Day along the coast. However, the weather will be noticeably cooler as a result of the low pressure system moving east.
Next week it looks like highs in the mid 80's with light northerly winds, at least early in the week.

Enjoy this wet weekend. While it puts a damper on the outdoor plans, it is some much needed rain to make up for last year! BUT be safe and keep an eye out for water covering roads if you are out and about through the day Friday and Saturday morning.
I'll update again if possible Friday mid-day, and Saturday to recap the event. Thanks for reading.

Flood Heavy Rainfall

Houston/Galveston April Climate Summary

By: LPerezIII, 1:52 PM GMT on May 03, 2012

April 2012 vs. April 2011
And a look Ahead

We all know 2011 was the year of the worst drought Texas has ever seen, at least since records began in the late 1800s. Many record high temperatures were broken across the state as well. This year started off with quite a bit of rain for southeast Texas, but how does April 2012 compare to April 2011 for the Houston/Galveston area? How does the performance so far compare to normal climate averages? And what are the expectations for the next few months?

For that information, we can check the local climatology on the National Weather Service Houston/Galveston website.

We're going to look at the following statistics: The Highest and Lowest temperature for the month, the average high and low temperature, the amount of rainfall for the month, and records set in these areas since the tracking of records began in 1875.

Galveston, TX April 2012 April 2011
Highest Temperature 86 95*
Lowest Temperature 58 55
Avg. High 80 81
Avg. Low 69 69
Rainfall Amount 1.99 Inches 0.12 Inches

*Current April Record - Set on 4/27/2011

In Galveston for April there is not a huge difference in the average high and low temperatures, but April 2011 sure got warm at the end of the month setting a new April record high of 95 degrees. It was also extremely dry with only 0.12 inches for the month. This year is looking better, and much more normal. For April 2012, the island recorded 1.99 inches of rainfall. Let's hope we get the same performance or better for May!

Houston, TX April 2012 April 2011
Highest Temperature 88 93
Lowest Temperature 52 41
Avg. High 83 86
Avg. Low 64 64
Rainfall Amount 3.28 Inches 0.11 Inches

Houston had much of the same story as Galveston - they are close neighbors, so that is the expectation to an extent. Thankfully, 3.28 inches of rain fell in April in Houston.

Interestingly, both the record highest and lowest temperatures for April in Houston (IAH) occurred in 1987. A record April low of 31 degrees was recorded on 4/3/87 and a record April high of 95 degrees was recorded on 4/28/87. While I'm not entirely sure how often the record high and record low temperature for a given month, for one location, occurs in the same year I'd venture to say it is fairly rare.

The following two charts shows 2012's progress of climate (Temperature and Precipitation) as compared to the normal climate.

By the data contained in these two charts it looks like, temperature-wise, both Galveston and Houston are on track in the normal region. Galveston does show a slant toward overall warmer temps, but this is likely due to the warmer than normal water temperature that resulted from a rather mild winter and quick spring warm-up. Galveston's proximity to the water has a dramatic effect on temperature across the island. While most people just "know" this as the truth, the chart confirms this by the width of the temperature range as compared to Houston throughout the year. Take July for example; Galveston's normal temperatures in July range from just below 80 degrees to just below 90 degrees. Houston however goes from about 75 degrees to nearly 95 degrees. Houston has a larger temperature variation by about 9 degrees compared to Galveston thanks to the water temperature regulating Galveston's air temperature. It's no wonder a good majority of Houstonians like to visit the Island. It's a nice break from the heat of the city!

As far as precipitation, both locations are above normal for 2012, thus far. After the drought in 2011, all of TX could use the abundance of rain through the year. Let's hope it continues above normal.

Looking ahead, the following map shows the three-month outlook for temperature Below (blue) or Above (orange) the average temperatures.

For our region, southeast Texas, there is a 40% of Above normal temperatures. This map, generated by the Climate Prediction Center, takes into account too many variables to cover here, but a big one is El Nino/La Nina, and the consensus is that El Nino is developing which will lead to higher than normal temperatures across the southern U.S.

The next map is the same as above but for Precipitation.

For May-June-July the Climate Prediction Center is leaning towards an Equal Chance of a Below Normal, Normal, or Above Normal amount of rainfall. Only the northwest US has a below normal probability of 30-40%. Again, this is typical El Nino pattern.

Overall, it is shaping up as a better, wetter, more consistent year than 2011 for Texas.

Enjoy the weather through the weekend. Next significant chances for rainfall will appear mid-week next week.

I'll continue to update every Thursday until the weather demands more attention.

Thanks for reading.

Climate Summary Houston Climate Galveston Climate

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Weather Spectrum

About LPerezIII

I have a passion for Mother Nature's fury, serenity, and beauty. I express my soul through my music and photography. B.S. in Meteorology from TX A&M.

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