Danielle a hurricane; TD 7 forming off coast of Africa
Hurricane Danielle has stopped intensifying and is now looking a bit ragged this morning, but remains a respectable Category 1 hurricane with 80 mph winds. The intensity of Danielle's heavy thunderstorms has waned in the past few hours, and the organization of the storm is less impressive. This is probably due do strong upper-level winds out of the west that are creating a moderate 10 - 20 knots of wind shear, and injecting some of the dry air from the Saharan Air Layer (SAL) that surrounds Danielle. Danielle is over warm 28°C water, but is far from any land areas.
Figure 1. Morning satellite image of Tropical Storm Danielle (left side of image) and the forming Tropical Depression Seven (right side of image.)
Forecast for Danielle
A powerful trough of low pressure over the mid-Atlantic Ocean will begin to pull Danielle more to the northwest by Wednesday, keeping Danielle well to the east of Bermuda. Most of the models predict that this trough will be strong enough to fully recurve Danielle out to sea. It is possible that Danielle could eventually threaten Newfoundland, Canada, but it currently does not appear that any other land areas will be at risk from this storm. History suggests that a storm in Danielle's current location has only a 20% chance of making landfall on the U.S. East Coast. If Danielle passes east of Bermuda, as forecast, these percentages drop to less than 5%. As far as intensity goes, it is looking unlikely that Danielle will attain major hurricane status (115+ mph winds.) There is enough dry air and wind shear affecting the storm today that it will take several days for the storm to recover its strength, making it less likely the storm can hit Category 3.
The formation of Danielle is remarkable in this it was successfully forecast by the GFS model nearly two weeks in advance. The ECMWF and NOGAPS models also did a good job of predicting Danielle's formation a week in advance. The models are getting better and better each year at forecasting genesis of tropical cyclones, though a successful 1-week forecast of genesis is still a rarity. For example, none of the models foresaw the development of 96L until just 3 - 4 days ago.
Figure 2. Plot showing historically the percent chance of a tropical cyclone in a given location impacting the U.S. East Coast. For storms in Danielle's current position (orange hurricane symbol), about 20% of them go on to hit the U.S. East Coast. For storms in 96L's current location (red circle with a "?" in it), the odds are also 20%. Image credit: Bob Hart, Florida State University.
96L (soon to be Tropical Depression Seven)
Satellite images suggests that a tropical wave (96L) that emerged off the coast of Africa yesterday morning has developed a closed circulation, low-level spiral bands, and an increasing amount of heavy thunderstorms. While this morning's ASCAT pass does not show a clear closed circulation, satellite estimates of 96L's strength support calling this a 30 mph tropical depression. It is likely that this storm will be designated Tropical Depression Seven later today. 96L is already bringing heavy rain and strong, gusty winds to the southern Cape Verde Islands. Winds were sustained at 26 mph at Mindelo in the northwest Cape Verde Islands this morning, and 24 mph at Praia, the station closest to the center of 96L. Both stations were reporting widespread dust, due to strong winds blowing Saharan dust from the coast of Africa. However, water vapor satellite images show that only a modest amount of dry air is accompanying this dust, and dry air is currently not a major detriment to 96L. Wind shear is about 10 - 20 knots, and sea surface temperatures are warm, 28°C.
Forecast for 96L/Tropical Depression Seven
Wind shear is predicted to remain low, 5 - 10 knots, for the next four days. SSTs will cool a bit to 27°C by Thursday, but this is still above the 26.5°C threshold for hurricane development. Dry air will probably be the main inhibiting factor for 96L. Most of the intensity forecast models bring 96L to hurricane strength by four days from now, and this is a reasonable forecast. 96L should become Tropical Storm Earl later today or on Wednesday, and will probably bring sustained winds of 40 mph to the southernmost Cape Verdes Islands tonight and Wednesday.
The long range fate of 96L remains unclear. The storm is being steering by the same ridge of high pressure steering Danielle, and will initially follow a track similar to Danielle. 96L may encounter the cold waters stirred up by Danielle at times this week, inhibiting development. As 96L approaches the central Atlantic five days from now, the storm will encounter the same mid-Atlantic trough that will be steering Danielle, and 96L should turn more to the northwest. It is unclear at this point whether this trough will be strong enough to fully recurve 96L out to sea, east of Bermuda. This will, in part, depend upon how strong Danielle gets. A stronger Danielle is likely to create more of a break in the ridge of high pressure steering 96L, encouraging the storm to turn north and recurve out to sea. A weaker Danielle will make 96L more likely to miss recurvature, and follow a track to the west or west-northwest towards the U.S. East Coast early next week. History suggests that a storm in 96L's current location has only a 20% chance of making landfall on the U.S. East Coast.
When will the Caribbean and Gulf of Mexico get active?
The large scale atmospheric circulation over the Caribbean and Gulf of Mexico currently features relatively dry, stable, sinking air. This is due, in part, to the Madden-Julian oscillation (MJO). The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The latest MJO forecast from the GFS model calls for the wet phase of the MJO to move into the Caribbean during the first week of September. However, keep in mind that forecasts of MJO activity 1 - 2 weeks in advance are not very skillful. The GFS model forecast of MJO activity made two weeks ago did fairly well for the first week, but poorly for the second week of the forecast.
Tropical Storm Frank spares Mexico
Over in the Eastern Pacific, Tropical Storm Frank has moved away the coast far enough from the Mexican coast to no longer pose a heavy rainfall threat, and all tropical storm warnings have been dropped.
"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog during the show. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. I'll focus on Danielle, Earl, and Frank, and discuss the possibilities of a hyperactive Atlantic hurricane period coming during the first week of September.
Today's show will be 30 - 45 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.
Jeff Masters
Reader Comments
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then there was three
And 96L in front of it. The odds appear to be increasing.
Mine was far more subtle :)
That nick... that comment... what can you say :)
Half the models now don't recurve Danielle she may end up being a threat to the US
xx/xx/96L
MARK
12.56N/28.13W
Half the models don't show recurve ... the glass is half empty?
Cloudsat hit just right of center of Frank earlier today.
He's got the mall.
Nothing touching..... YET
Tropical Cyclone Advisory #14
TROPICAL CYCLONE FRANK (EP092010)
3:00 AM UTC August 25 2010
================================
SUBJECT: "FRANK" Weakens A Little And Moves Away From The Southwestern Coast Of Mexico
At 3:00 AM UTC, Tropical Storm Frank (992 hPa) located at 16.0N 102.9W or 130 NM south southwest of Lazaro Cardenas, Mexico has sustained winds of 55 knots with gusts of 65 knots. The cyclone is reported as moving west northwest at 8 knots.
Storm Force Winds
================
55 NM from the center
Forecast and Intensity
=========================
24 HRS: 17.1N 105.9W - 60 knots (Tropical Cyclone)
48 HRS: 18.3N 109.3W - 65 knots (SVR Tropical Cyclone SSHS-1)
72 HRS: 19.5N 111.8W - 60 knots (Tropical Cyclone)
As an aside, a few days ago in ECF, a truck was driving down a country road after a storm and a huge pine tree fell on the cab as it drove by. Killed the passenger and seriously injured the driver. Talk about a freak accident....
Funktop seems to indicate a complete eyewall.
It's WHICH models don't recurve her that interests me--the GFS is an important one to watch. But, it only predicts no back-eastward movement for the next 120 hours...no individual ensemble member of the GFS has it actually reaching (yet).
I was worrying earlier this might happen since it went down to tropical storm status instead of becoming a cat3 that was previously thought. However, she should intensify more so maybe models with shift. I could be wrong about this, but I thought the stronger she was the more north it would go.
The GFS triplets are a particularly nasty notion.
ALERT ATCF MIL 96X XXX 100824180000
2010082418
13.0 334.6
14.7 328.2
100
13.0 334.7
250100
1008250100
1
WTNT21 KNGU 250100
MSGID/GENADMIN/NAVMARFCSTCEN NORFOLK VA//
SUBJ/TROPICAL CYCLONE FORMATION ALERT//
RMKS/1. FORMATION OF A TROPICAL CYCLONE IS POSSIBLE WITHIN 100NM
EITHER SIDE OF A LINE FROM 13.0N 25.4W TO 14.7N 31.8W OVER THE
NEXT 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF A NUMBERED
TROPICAL CYCLONE WARNING AT THIS TIME.
2. A 1050 ZULU ASCAT PASS SOUTH OF THE CAPE VERDE ISLANDS
SHOWS AN ELONGATED AREA OF CYCLONIC CIRCULATION. CURRENT REGIONAL
MODELS ARE SHOWING INTENSIFICATION OF THIS LOW OVER THE
NEXT 24HRS. THIS, IN CONJUNCTION WITH WARM SEA SURFACE TEMPERATURES
OF 86 TO 88 DEGREES FAHRENHEIT SHOULD HELP TO ENHANCE THE DEVELOPMENT
OF THIS TROPICAL FEATURE.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO A WARNING OR ALLOWED TO
EXPIRE BY 260100Z AUG 2010.//
Average Position Error (nm) for core models
model Error Trend 24hr Error 48hr Error 72hr Error Day 4 Error Day 5 Error
AEMN INCREASING 73.2 71.3 76.2 74.7 -1
OFCL INCREASING 92.1 120.2 74.6 -1 -1
LBAR DECREASING 100.7 160.9 244.8 225.6 -1
MM5E INCREASING 101.8 157.5 211.6 -1 -1
MM5B INCREASING 106.9 157.3 143.3 208.8 -1
BAMD DECREASING 117.3 140.6 185 129.4 -1
GFDL INCREASING 127.5 95.4 110.6 183.2 -1
HWRF INCREASING 138.6 130.2 143.9 208.1 -1
KHRM DECREASING 158.7 324.2 293.5 -1 -1
NGPS INCREASING 193.9 267.6 336.5 357.1 -1
Paint NEVER dries here! Lol. Be careful where you sit.
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