Friday, October 7, 2005

Super Soaker Scenario


The Washington DC metro area is being soaked with drought-busting downpours today. As of 2pm, the Official Bucket had picked up 1.23", but a mid afternoon lull was broken by a new wave of moderate to heavy rain moving up I-95. This new batch reduced visibilities as low as 1/4 mile and added 0.56" more rain by 4pm. This amount has already broken the daily record for October 7 of 1.60" in 1965. Rain is continuing, but it was light in the latest report, with another 0.24" added as of 5pm. The Doppler radar estimate of total rainfall shows some amounts in the 5" range in the higher elevations to the west.

Following the latest band of heavy showers, there will be another relative lull in the rain later this evening, but there is plenty more tropical moisture available to continue the festivities through much of the weekend. Jason has laid out a chronology of events in his earlier post. Stay tuned for updates through the weekend.

Tropical Beat

The low pressure area which was over western Cuba yesterday has weakened, but the moisture from it is moving north and bringing a lot of rain to Florida.

A low about 425 miles northeast of the Leeward Islands has been designated a "Special Feature" by the National Hurricane Center, and it has some potential to develop within the next 36 hours.

There are several tropical waves located from the central Caribbean eastward to the eastern Atlantic.

More Divine Wind

You can hear an interview with Dr. Kerry Emanuel, author of "Divine Wind", which was mentioned in yesterday's afternoon update, at the website of the Living on Earth radio program. There is also a transcript of the interview. Prof. Emanuel was interviewed on NPR on Sept. 6. The book is the text for a seminar being given this semester at UCLA. Lecture materials are being posted on the class website. If you happen to be in Bermuda next Wednesday, Prof. Emanuel is presenting a lecture at the Bermuda Biological Station for Research.

Thursday, October 6, 2005

Tammy and the Doctor


The National Weather Service has issued a Special Weather Statement (scroll down to 1103 am) for potential heavy rain and flooding this weekend and a Flood Watch from Friday morning through Saturday afternoon.

Parched lawns and gardens throughout the Washington DC metro area are gazing longingly southward this afternoon in hopes of receiving some rain from the remnants of former Tropical Storm Tammy. By mid afternoon, some very widely scattered showers had appeared, mainly to the west, where Leesburg was reporting heavy rain at 2pm. This was short-lived, however, as only 0.03" fell. The most intense activity was on the Eastern Shore, from the Bay Bridge southeastward to the southwestern corner of Delaware. By 3:00, many locations were reporting at least partly sunny skies and temperatures which were pushing close to or above 80; the official reading was 81 at 4pm. Dewpoints were at the "tropical" level on the muggometer, ranging from a few high 60s to the low 70s. As an upper-level trough approaches from the Midwest, the flow over our region will change from light and variable this morning to moderate (near 50 knots) from the south and southwest, helping to bring some of the much-needed tropical moisture left over from Tammy.

Tonight and Tomorrow

Tonight, the chance of rain will increase to 50% by morning as low temperatures reach only down to about 68. Rain is likely tomorrow (near 100%) with highs around 73.

Tropical Beat: Tammy

The last tropical advisory on the remnants of Tammy was issued at 11am this morning with the center of circulation over extreme southeastern Alabama. This was moving west at about 12 mph. It could even move southwest and out over the Gulf of Mexico, but regeneration is not likely. Meanwhile, the moisture originally associated with the storm is moving to the north and northeast, bringing heavy rains as far north as central North Carolina.

Further south, a weak low pressure area over western Cuba was poorly organized and unlikely to develop further, but it will bring more rain to Florida as it moves northward.

In the central Atlantic, almost 1200 miles east of the Windward Islands, a large tropical wave is being watched for potential development over the next couple of days.

Tropical Beat: The Doctor
Divine Wind
"Divine Wind", a book about "The History And Science Of Hurricanes", was delayed from its original publication date but is now available. The author is Dr. Kerry Emanuel, meteorology professor at MIT, and the book has been getting rave reviews; it is already out of stock at the publisher. Dr. Steve Lyons, the Weather Channel hurricane expert, said:
"Until I read Divine Wind I had never found a book unique enough to contain the science and the history of hurricanes accented with the prose, songs and art about them. It provides fascinating accounts of notorious hurricanes that have changed history. With sound science it educates readers about how hurricanes form, how strong they can get, how they are tracked and what types of devastation they can cause. Both meteorologist and non-meteorologist will be captivated with it. I couldn't put the book down, anxious to absorb the next fascinating piece of hurricane history. Divine Wind is a must read for everyone interested in how hurricanes work, how they have molded coastal city history and how they have affected wars.
Here are some other reviews: The book's website has links to downloadable images, supplementary material, a hurricane model computer program (Fortran 77), and other hurricane resources.

Wednesday, October 5, 2005

Tammy Tell Me True

All eyes are on minimal Tropical Storm Tammy today for the chance to bring us some drought-breaking rain. But first, let's clear up the October Urban Legend. It may be because perfect warm, dry days like today are so memorable that it seems as if October is usually a dry month. In fact, October is a transition month between the normally wetter summer and the normally drier winter. The record shows that October has only the 7th driest long-term average rainfall of all the months of the year in Washington DC weather history. That's right, at 3.22", October is (just barely) wetter than January's 3.21". The driest month is February, with 2.63". Of course, February also has only 28.25 days on average, but even accounting for that, October is nearly 12% wetter than February. The months which have less total precipitation than October are: January, February, April, June, November, December.

Currently, temperatures are near or even a little above 80 in the metro area under sunny skies.

Tonight and Tomorrow

Tonight should see lows in the low 60s with increasing cloudiness toward morning. Tomorrow will be mostly cloudy with highs in the upper 70s.

Tropical Beat

Tropical Storm Tammy developed just off the Florida coast this morning. This is only the 4th time there has been a 19th "named" storm in a single year, and it is the earliest one by almost 3 weeks. The others formed on 12/07/1887, 10/25/33, and 10/27/95 ("Tanya").

At 2pm, Tammy was centered only 20 miles northeast of Daytona Beach, moving north-northwest at 14 mph. By the 5pm advisory, it was 15 miles north-northeast of St. Augustine. Maximum winds had increased slightly to 50 mph, but tropical storm winds extended as much as 260 miles from the center. The strongest winds and heaviest rains were mainly to the north and east.

On the forecast track, the storm should be a depression in central Georgia by tomorrow evening. That's when things start to get interesting for us. There is a lot of moisture associated with this storm, and indications are that it will be moving northeastward as the high pressure ridge now over us moves slowly eastward off the coast. The global forecast model ("GFS") from this morning's data has some light rain reaching the area as early as tomorrow afternoon, but the heavier amounts don't arrive until Friday morning. The latest model ("NAM") output from this afternoon's data delays the arrival of precpitation until midday Friday and keeps the heaviest amounts in eastern North Carolina and central Virginia. The official NWS precipitation forecast ("QPF") made early this afternoon has 2" to 3+" of rain in the local region for the 24 hours from tomorrow evening through Friday evening.

At this point, I don't have a lot of confidence in either the exact timing or the amount of rain, but this is the best chance we've had in at least about 6 weeks to get some serious precipitation in the Washington area. Stay tuned tonight and tomorrow for updates as the situation develops.

Monday, October 3, 2005

Falling Back to Summer

Yesterday's official high of 82 was consistent with the long-term average for the early days of September, and temperatures this afternoon are approaching similar readings in the Washington metro area. Fortunately, dewpoints in the mid 50s are keeping comfort levels more in line with fall than summer.

Tonight and Tomorrow

After lows tonight in the low 60s, some clouds tomorrow should keep temperatures a couple of degrees cooler than today.

Tropical Beat

As Jason predicted below, Stan has been revived by the warm waters of the Bay of Campeche and is now a tropical storm again with maximum winds of 55 mph. An Air Force reconnaissance flight was on the way to investigate early this afternoon. Some strengthening is expected, and Stan could make landfall on the Mexican Gulf Coast as a hurricane.

The area of more interest for the U.S. is a low-pressure trough which extends through the central Bahamas. This has the potential to develop as it moves westward, and a NOAA flight is scheduled for tomorrow.

Bizarro Weather World

The WaPo, which has rarely shown much of an inclination to take science seriously, wastes an entire half-page of valuable A-section real estate today on the latest crackpot scheme for "controlling" hurricanes. This kind of idea, which normally hangs out in the sub-basement along with the perpetual motion machines, cold fusion, and the recipes for transmuting lead into gold, gets trotted out every few years, usually when a major weather disaster has captured the public's attention. This particular plan involves firing off large numbers of jet engines on barges in the path of the storm. The promoter is asking for a mere $10 million to perform an experiment.

Here's an idea: Walk over to Staples, buy a No. 2 pencil for about a dime, and do some arithmetic on the back of the envelope from your latest credit card offer. Prof. Kerry Emanuel, a meteorology professor at MIT who has actually done research on the energy budget of tropical storms, is way too polite when he says, "I hate to sound pessimistic, but Moshe's strategy requires many orders of magnitude of energy more than what he's talking about, and the backfires would have to be almost as strong as the hurricane itself." Unfortunately, even this relatively mild rebuke is buried near the bottom of the second column (second page of web version).

Note to WaPo "science" reporters: It's time to learn your Powers of 10. And while you're at it, why don't you cover something we actually can control, like, oh, I don't know, maybe CO2 emission?

Afternoon Update is taking a break tomorrow, but will resume on Wednesday.

Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.