Tropical Depression Fifteen forms in the Caribbean
Tropical Depression Fifteen is here, and is destined to become Tropical Storm Matthew by late this afternoon or this evening. An Air Force hurricane hunter aircraft left the storm near 2pm EDT this afternoon, and on their final pass through the strong northeast quadrant of the storm, found a substantial area of surface winds of 40 - 45 mph with their SFMR instrument. Top flight level winds at 500 feet were 48 mph. These winds support upgrading TD 15 to Tropical Storm Matthew. Satellite loops show that TD 15's heavy thunderstorm activity continues to increase in intensity and areal coverage, with several respectable low-level spiral bands in evidence. There is some dry air to the northwest of TD 15, but it is currently not significantly affecting development.
Figure 1. TD 15 at 11:50am EDT 9/23/10, as seen by NASA's Terra satellite.
Forecast for TD 15
An upper-level high pressure system lies to the west of TD 15, near the coast of Nicaragua. The clockwise flow of air around this high will bring a moderate 10 - 20 knots of wind shear over TD 15 today and Friday. There is some dry continental air lying to the northwest of TD 15, and this shear may be able to drive dry air into the storm, slowing intensification and keeping TD 15 below hurricane strength through Saturday morning. By Saturday afternoon, TD 15 will move more underneath this upper-level high, causing the shear to decline. The SHIPS model forecasts that shear will fall to the low range, 5 - 10 knots, Saturday through Monday. This drop in shear should allow for intensification of TD 15 into a hurricane, if the center stays more than 50 miles offshore.
The future track and intensity of TD 15 depends critically upon the storm's interaction with land over the coming days. If TD 15 misses making landfall in Nicaragua and Honduras, and instead skirts the north coast of Honduras, the storm is likely to intensify into a hurricane by Sunday, as indicated in the official NHC forecast. However, if TD 15 spends significant time over or barely offshore of Honduras, the storm will likely stay below hurricane strength. TD 15 is being forced just north of due west by a strong ridge of high pressure. This ridge will keep the storm moving at 15 mph through Saturday. On Sunday, a trough of low pressure diving southwards over the Eastern U.S. will weaken the steering currents over the Western Caribbean and cause TD 15 to slow and turn more to the north. TD 15 will begin a period of slow and erratic movement on Sunday that may last many days, as the storm wanders in the Western Caribbean and over Belize, Honduras, and Mexico's Yucatan Peninsula. If the center of TD 15 spends significant time over water, the storm could easily develop into powerful and dangerous Hurricane Matthew. If the center remains mostly over land, TD 15 will still generate extremely heavy rains over Central America, but remain below hurricane strength. By late next week, the trough of low pressure over the Eastern U.S. may lift out, allowing a ridge of high pressure to build in and force TD 15 westwards across the Yucatan Peninsula and into the Gulf of Mexico's Bay of Campeche. Alternatively, the trough of low pressure over the Eastern U.S. may amplify, drawing TD 15 northwards across Western Cuba and into Florida. A complicating factor may be the development of a new tropical depression in the Central Caribbean 6 - 8 days from now, as predicted by both the GFS and NOGAPS models with their latest 12Z (8am EDT) runs. The uncertainties in the long-range fate of TD 15 are high, and depend strongly on slight variations in its track that determine how much time the storm spends over land. One thing that is virtually certain is that TD 15 will generate very heavy rains over Nicaragua, Honduras, Belize, and Mexico's Yucatan Peninsula Friday through Tuesday that will cause dangerous flooding rains and life-threatening mudslides.
Tropical Depression Lisa
Tropical Depression Lisa continues to churn the waters of the far Eastern Atlantic. By Saturday night, upper level winds out of the west are expected to increase, bringing high wind shear of 20 - 45 knots over Lisa. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.
Elsewhere in the tropics
The remnants of Hurricane Julia are still spinning over the far Eastern Atlantic, and are generating some sporadic heavy thunderstorm to the north of the center of circulation. Julia's remains are being given a 10% chance of re-developing by NHC.
Hurricane Karl's moisture causing flooding in Minnesota, Wisconsin
A plume of very moist air associated with what was Hurricane Karl last week has surged northwards over the Central U.S. over the past two days. This moisture is now being lifted over a warm front draped over Minnesota and Wisconsin, and has generated flooding rains in excess of six inches in southern Minnesota this afternoon. Flood warnings and flood watches are posted for a wide swath of the upper Midwest today, including most of southern Minnesota, northern Wisconsin, and Michigan's Upper Peninsula. These types of rain events are called Predecessor Rain Events (PREs), because they typically precede the actual arrival of the rain shield of a tropical storm.
Figure 2. Radar estimated rainfall over Minnesota.
Next post
I'll have an update on TD 15 Friday morning.
Jeff Masters
Neighbors help a driver to move his vehicle from the flood waters
Reader Comments
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With todays modern tools for meteorology there is still only a 31% chance at guessing where a tropical storm will be in 4 hours time, 8% chance at 24 hours. Let alone figuring the strength or atmospheric influences that play into the tracking. That pretty much makes this a giant guessing game, model are severely inaccurate and the Professionals always say "we will be keeping an eye on this storm for you" that translates into " I have no Idea whats going to happen in 6 hours". Nice, so what is the point of this blog? Bragging rights to the one who Guesses it right? The big I told you so? Kudos.
This all translates to WISH-CASTING. Leave it to the pros who are only scarcely correct.....
winds up to 45mph
thanks
You can try Biscayne National Park's concessionaire but its been blowing badly enough these past couple days they may stay in the Bay and not go to the reef which isn't as fun. Don't know about options further north.
Well, actually cold, cold, cold cloud tops. lol
The peak value is ~400 kr m^-2, but some modification of the color scale, and the same "waves" from the north through halfway down come out. As does the "squared" section in the NW corner. I think this is simply in the HWRF output. I'd call this a not useful intensity model.
The plot that spawned all of this HWRFian doubt:
WNW jog at the moment..
convection is wrapping around nicely over the center..
conditions still favorable for rapid intensification.. just needs to get a little more stronger at the surface to suck up for energy at a faster pace
Yeah, well what's in a word eh LOL
Still a lot of ECMWF ensemble members that are further left that the Euro operational.
Thanks Neapolitan. I'm in Colton, California. About an hour from the beach, an hour from the Mountains, and an hour from the desert. If I wasn't married, I'd have pickup, a jetski, an ATV and a windsurfer's board (whatever you call that.) Instead I have a minivan -- LoL.
Around here, they go on StormWatch (tm) if there's 1/4 inch of rain on the way!
Was just looking at that. Seems to me its trending alittle farther West, which could mean more land interaction.
All the way up the east coast is peppered with decent snorkeling. I stress decent in the shallows. Much better up the coast if your diving 50 to 100ft. Red Reef Park in Boca Raton is one of the better spots. Over the past several years they have been placing man made reefs up and down the coast to limit beach erosion.
I agree we should keep it clean.
Nice, thanks for the advice! I'm forwarding it all to my wife as she's in charge of the itinerary. I only wanted to go to Key West because my dad snorkeled there almost 50 years ago to the day when he was in the Navy.
Wrong...no evedence of this.
The fish are safe to eat!!!!!!!!!!!!
Looks interesting. "Experts". Not sure if I qualify
Thanks, I'll bring that up to my wife as well.
To keep it tropical: Now that Matt has a good CDO I can finally pick out his center... at least approximately. He's the first storm I've really seen develop when he started surrounded by a huge mess of disorganized convection. It seems these storms find it difficult to consolidate when it's popping all around. I don't pretend to know why though.
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