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Atlantic Tropical Weather Update 8/10/09

The Atlantic has been mighty quiet during the first two months of the 2009 Hurricane Season, in fairly stark contrast to the past few years.  Tropical wave after wave have crossed over Africa, only to fall apart over the Atlantic.  A number of these waves have subsequently redeveloped over the Eastern Pacific – Tropical Storm Enrique and Hurricane Felicia are the latest two named storms with T.D. 9-E becoming the latest tropical system to form.   By way of comparison, the Atlantic has seen only one T.D. this year, and that was way back in late May.  Note that this isn’t all that unusual: August is climatologically the month when tropical storms start to form with some regularity in the Atlantic, especially under El Nino conditions.

Well, two waves are transiting the Atlantic Ocean this week that are showing signs that the season may begin to see more activity.  The National Hurricane Center (NHC) has begun monitoring a cluster of storms south of the Cape Verdes Islands: Invest-99.  A satellite passed over this disturbance this morning and a closed circulation has almost formed.  Wind gusts of 45mph were detected in a band of thunderstorms on the southwestern portion of the disturbance.

Invest-99 isn’t in the best environment for tropical storm development.  Sea-surface temperatures are only moderately warm: 27-28°C, compared to the 28-31°C SSTs in the western Caribbean Sea.  Additionally, there is a large amount of dry air to the disturbance’s north right now, which came off of Africa along with the disturbance.  This air came from the Sahara and is very stable, very much unlike the moist, relatively unstable air from Equatorial Africa.

Invest-99 has a 30-50% chance of developing into a tropical depression in the next 48 hours.  Most model solutions keep the disturbance near 15°N for the better part of the next three days, after which a slight curve toward the northwest is possible.  That track would keep the storm well away from the Lesser Antilles in the 5-7 day range.  I will point out that the lack of disturbances this year also means the skill of models should be taken with a large grain of salt.  This season’s storm behavior has yet to be ascertained by even one storm near the tropics.  Until then, climatology or chance likely provides almost as much skill in predicting future storm motion.

In the span of time since this morning, a second area of potential tropical formation has come to light: a band of storms near the Windward Islands.  This westward moving disturbance is less defined than its cousin to the east.  It is closer to warmer SSTs, but also closer to a pretty hostile vertical wind shear environment.  As such, the NHC is giving it a <30% chance of development within the next 48 hours.

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Atlantic Tropical Weather Update 9/2/08

Lots of changes in the Atlantic basin since yesterday. Gustav has continued to weaken, from Hurricane strength down through Tropical Storm and is a Tropical Depression this morning over the TX/LA border. Hanna strengthened to a Hurricane, then weakened back to a Tropical Storm. Then, Tropical Depression Nine formed between the Leeward Islands and the Cape Verde Islands. Then T.D. 9 strengthened and was named Tropical Storm Ike. Then T.D. 10 organized from Invest-99 between the Cape Verde Islands and Africa. Development didn’t stop there: T.D. 10 strengthened and Tropical Storm Josephine formed. That’s all in less than 18 hours. The Atlantic basin is pretty much full of storms.

Let’s start with Tropical Depression Gustav’s vitals: center located at 31.7N, 93.4W; maximum sustained winds of 35mph; moving NW @ 10mph; minimum pressure of 985mb. Gustav’s main threat now is lots of rain that could cause flooding. A secondary threat remains tornadoes. Gustav is forecasted to curve toward the northeast over the next five days, but the distance covered shouldn’t be too great. He should move into northeast Texas, southeast Oklahoma, then western Arkansas by early Friday morning.

Yesterday, Hanna was a Category 1 hurricane. She stalled off the eastern side of the Bahamas as her steering currents weakened. She followed by weakening back to a Tropical Storm, where she remains this morning. Steering has picked back up this morning and Hanna is back on the move. Her vitals: center located at 21.0N, 73.5W; maximum sustained winds of 70mph; moving WSW @ 5mph; minimum pressure of 987mb.

Hanna is forecasted to begin moving back toward the northwest later today, then continue that general movement through the next few days. She is also forecasted to regain hurricane strength by tomorrow afternoon as she moves through the Bahamas. From Thursday to Friday, Hanna should be moving by the east coast of Florida, but no landfall is expected on that state. Sometime during the day on Friday, Hanna is expected to come ashore along the Georgia border, an event that is very rare due to the orientation of the coast and the climatological movement of storms along the eastern seaboard. By the time Hanna reaches the Georgia/South Carolina border, the model track solutions diverge. Some show her moving into West Virginia before curving toward the northeast. Some show her moving through the Carolinas before turning northeast and along the east coast. That’s some time away, so the details will have to wait.

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Atlantic Tropical Weather Update 9/1/08

[Update 11:45A MDT]:

Tropical Storm Hanna has strengthened to a Category 1 hurricane.  An Air Force reconnaisance plane investigating the storm found winds strong enough at flight level to support the decision to characterize the storm as a hurricane.  Her updated vitals:

Center located at 22.4N, 72.6W; maximum sustained winds of 75mph (just over category 1 threshold); moving WSW @ 4mph; minimum pressure of 985mb (9mb less than the previous update).  The lowering pressure should allow Hanna to continue to slowly strengthen into a moderate Category 1 hurricane.  The intensity forecast has been updated to reflect this status in the short term.  At this time, the models are not indicating a strengthening to Category 2 strength.

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Hurricane Gustav made landfall within the past hour or two (currently 9:30A MDT) on Louisiana’s southern coast, near Cocodrie, Louisiana, which is south of Houma, Louisiana.  He made landfall as a strong Category 2 storm.  Reports are coming in that levees in New Orleans, to Cocodrie’s north, are being overtopped by the storm surge and waves.  I’m sure additional reports will come in throughout the day.  His vitals:

Center located near 29.2N, 90.8W; maximum sustained winds of 110mph; moving NW @ 14mph; minimum pressure of 955mb.  Those sustained winds are the threshold between a Category 2 and Category 3 storm.

Gustav’s future looks radically different than it did last night in the long-term.  He is expected to slow down over the next day or so as he moves across Louisiana and eastern Texas, weakening the entire way.  Between Tuesday and Wednesday, Gustav should turn toward the north (instead of the south, as was indicated last night) and his forward speed should continue to decrease.  Friday could see Gustav still moving slowly to the north into Oklahoma.  By the end of the week, another synoptic trough should be moving across the United States.  That trough right now looks less robust than the one currently making its way from west to east, but Gustav’s remnants should get caught up in the larger scale flow and advected out of the Texas/Oklahoma region.

So beyond additional levee failures in the New Orleans area, the main threat from Gustav will gradually shift toward flooding as he stalls and rain falls over the same area for many hours.

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Atlantic Tropical Weather Update 8/4/08

Tropical Storm Edouard continued to organize himself last night as he moved westward in the Gulf of Mexico.  The convection that was isolated on its southern half has balanced itself out to all quadrants.  Upper-level wind shear decreased overnight, which should allow for further strengthening today.  The Gulf waters are plenty warm, though fairly shallow where Edouard is forecasted to be.  His vitals:

28.2N, 90.6W; moving W @ 8mph; maximum sustained winds of 45mph; minimum pressure of 1002mb.

The track forecast still has Edouard’s center coming ashore southwest of Galveston, TX.  Due to his motion leading up to that event and the arrangement of the Texas/Louisiana, however, the landing could occur hundreds of miles away from there.  Tropical Storm force winds extend some distance away from the center of the storm.  The threat then is those winds and the accompanying rain bands now seen spiraling around the center on radar imagery.  Strengthening to Category 1 hurricane status is not out of the question, but it’s not very likely to occur either.

Invest-90 puttered out overnight.  It isn’t present on satellite imagery today in any recognizable way.  This wave looked more impressive to me long-term than the other wave still in the Atlantic.  It goes to show just how fickle tropical storm development can be.

Invest-99 is still tracking across the Atlantic.  He’s located at 19.5N, 54.3W, moving WNW now.  Winds are estimated at 30mph.  The chances of development are still less than 20%.  I-99’s forecasted movement is toward the NW, then NE to the southeast of Bermuda.  This track would be somewhat close to Hurricane Bertha’s last month.  Models are forecasting intensification over the next five days.  They’ve been doing this during I-99’s lifetime so far and it hasn’t happened.  The main difference now is I-99 is located over warmer waters.  Stay tuned.


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Atlantic Tropical Weather Update 8/3/08

The three disturbances in the Atlantic/Gulf of Mexico haven’t changed much since yesterday. Starting from the most likely to impact the U.S. directly first:

Invest-91 is centered approximately at 28.3N, 88W. It’s moving W and has estimated sustained winds between 30 and 35mph. An Air Force Reserve hurricane hunter aircraft is on its way to the system to determine if it has a closed surface circulation. If it does, it will be classified as a Tropical Depression. Model forecast tracks are in much better agreement today that the system will likely come ashore southwest of Galveston, TX. At what strength it does so remains to be seen. The NHC is giving it a >50% chance of developing to a T.D.

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[Update 4:15P MDT]: As expected, Invest-91 became organized enough to be considered a Tropical Depression this afternoon.  Then it strengthened even more – we now have Tropical Storm Edouard in the Gulf of Mexico.  There is a better fix on the central low, currently located at 28.1N, 88W, very close to the estimate from earlier.  His sustained winds are now 45mph.  Tropical Storm Edouard is expected to continue strengthening as he moves west at 6mph.  For now, convection is largely limited to the southern portion of the storm.   That will change as Edouard gains steam.

A Tropical Storm Warning has been issued for the eastern half of Louisiana’s southern coast.  A Tropical Storm Watch has been issued for the western half as well as the Texas coast to Port O’Connor (between Corpus Christi and Galveston).  The entire Texas and Louisiana coasts are going to feel the brunt of this storm.  Landfall is expected Tuesday in the late morning to early afternoon.

This storm has likely already caused the shut down of oil drilling and refining operations in the northern Gulf.  That is bad news for oil for the next week.

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Invest-90 is centered at 11.6N, 34W. It’s also moving W and has estimated sustained winds of 30mph. Model track forecasts largely agree that the disturbance will pass over the Leeward Islands at about 15N in 3+ days. Model intensity forecasts indicate that could happen as a Tropical Storm or weak Category 1. I’m still not convinced the system will strengthen that much by that point in time. After entering the Caribbean Sea, the system is forecasted to take a NW track and could impact the island of Hispanola. Time will tell. The NHC has given this system a <20% chance of development.

Invest-99 moved further west yesterday than it did northwest. It’s current location is 19.3N, 52.4W. Currently, it’s also moving to the W and has estimated winds of about 30mph. It should begin moving toward the north-west in the next 12-24 hours, with a turn toward the north in 24-36 hours. Model intensity forecasts indicate that the system could strengthen quickly in 1-2 days. That is possible since it finds itself over warmer waters now (close to 80F) and a slightly more conducive wind shear profile. The NHC has given this system a 20-50% chance of development.

There is another cluster of storms moving off the west coast of Africa at about 9N.

Images of sea surface temperatures indicate a cool-pool where Hurricane Bertha slowed down south of Bermuda. Recent climate-hurricane research postulates that tropical storms act as energy distributors (high energy from the equator replacing low energy from the pole) in much the same way that mid-latitude systems we in the United States are used to experiencing do. In this case, warm surface waters were evaporated and then condensed in the atmosphere. This more or less transferred warmth from the equator pole-ward. Cooler sub-surface waters rose to replace what Bertha evaporated and both parts of the system were moderated. Interesting stuff.


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Science Goodies 8/2/08

The tropical Atlantic has been quiet for a while. A few tropical waves have exited Africa only to dissipate in unfavorable conditions over the open ocean. Two waves recently moved off that might bear watching.

Invest-90 has the better long-term chance of development, I think (the link may not be up forever). It’s the more southerly of the two, located about 11N, 27W. Its maximum winds are 30mph and is moving W @ 20mph. There isn’t any circulation associated with this system yet. I don’t buy the model intensity forecast – they’ve strengthened everything out there all season long so far into tropical storms and then hurricanes. I think we’re a few days away from seeing it organize. Then again, things can happen quickly out there. The tracking forecast is good for this system – the models keep it between 10N and 15N for five days, at which point it could pass over the Lesser Antilles. After that, a more NW course is forecasted through the Caribbean.

Invest-99 has the better short-term chance of development. It’s located about 19N, 43W. Cooler ocean temperatures exist there currently than they do under Invest-90. But some slow rotation associated with it. The model solutions are in good agreement that it will continue moving NW across the Atlantic before turning NE at about 25N, 60W. Model intensity forecasts make it a Storm in about a day, reaching strong Tropical Storm force within five days. I’m not sure that will be the case. The system is encountering a region with fairly strong vertical wind shear, so it will have to fight to develop.

[Update 1:45P MDT]: Things just got a little bit more exciting. A new system is being watched: Invest-91. It’s centered at about 29.5N, 87W: in the Gulf of Mexico just south of the Florida panhandle. Waters there are plenty warm as they’ve been undisturbed the entire season so far. It looks like it was the trailing feature of a surface trough. Visible satellite image. Infrared satellite image. A good burst of convection is apparent near the surface low. Weak upper outflow can also be seen. The system is too far out to sea to get good radar imagery from it. Mid- to high-level steering is essentially SW to W. Model track forecasts see this continuing – they agree that I-91 will move through the northern Gulf for a few days before coming ashore. It looks like that could happen anywhere from west of Timbalier Bay, LA to Corpus Christi, TX. Needless to say, the exact landfall point is pretty irrelevant. If this system grows and strengthens, heavy rains and flash flooding is likely to occur over a wide area. With the large ridge in place over the U.S., this system should move inland until dissipation later in the week.

Invest-99 has two more model solutions available. They keep the storm more to the south on a westerly heading over the next couple days than the other three models. We’ll see which pattern is correct over the next day.

For what it’s worth, the NWS thinks Invest-90 and Invest-91 have the best chances of development: 20-50% over the next day. Invest-99 has <20%.

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A large lake has been confirmed to exist on Saturn’s moon Titan. Ontario Lacus is located at Titan’s south pole. You can find the details in the July 31, 2008 issue of Nature. The lake, like Titan’s atmosphere, is composed of hydrocarbons. A beach, left behind by evaporating ethane, is visible in the imagery. Important findings continue to be made by Cassini.

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SEPA has released its first annual Top Ten Utility Solar Integration Rankings (large pdf). There’s lots of good information in this report and I’ll write more on its significance to Colorado.