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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Matthew - Who knows... going into Box #2
AOI
TS BUSTED FORECAST ALIBI
WUmail pending.
You guys are missing one major problem if it stalls or runs along the coast.... the rainfall will be measured in feet... not inches
Taco, go eat a burrito homes!
see the two lows in the same isobar? be intersesting to see if one breaks away from the other.
exactly,this would be a bad scenario in terms of lost lives
It is literally a disaster unfolding before our eyes...and people cant see it.
And Belize is such a beautiful country.
nottMatthew
8AM Jury Duty. Never been called before! Looking forward to that also.
Greetings,
The COMET Program is pleased to announce the publication of the first distance learning course in our new NWP training series: Effective Use of NWP in the Forecast Process, accessible at http://meted.ucar.edu/dl_courses/nwp . The home page for the training series has a tab for each course, and for an introduction. The Introduction is a short lesson providing an overview of the series, including the goals and philosophy of the series, oriented toward adding value to NWP guidance.
Course 1: NWP Basics and Background, builds a foundation for forecasters to understand and interpret the forecasts produced by NWP models. The course contains 10 lessons, including an update of the six lessons in the COMET NWP Course produced ten years ago:
Model Fundamentals %u2013 version 2
Impact of Model Structure and Dynamics %u2013 version 2
How Models Produce Precipitation and Clouds %u2013 version 2
Influence of Model Physics on NWP Forecasts %u2013 version 2
Intelligent Use of Model-Derived Products %u2013 version 2
Understanding Assimilation Systems: How Models Create Their Initial Conditions %u2013 version 2
These lessons have been streamlined to focus on concepts and content specifically applicable to operational forecasters (8-10 hours total, plus optional content).
In addition, three new lessons have been developed and a fourth is under development:
Introduction to NAEFS, the North American Ensemble Forecast System, a 60-minute webcast on the new combined Canadian Meteorological Center and U.S. National Center for Environmental Prediction%u2019s (NCEP) global ensemble forecast system. The lesson emphasizes application of post-processed products in cold and warm season examples, and covers ensemble system configuration and product interpretation.
Effective Use of High-Resolution Models, a 90-minute web lesson covers the capabilities and limitations of high-resolution models run without a convective parameterization. It emphasizes issues of predictability and interpreting forecast output as event predictions instead of point forecasts. The lesson also introduces convective mode diagnostics such as updraft helicity.
Bias Correction of NWP Model Data, a 45-minute web lesson discussing the fundamentals of bias in NWP models, its sources, and three ways in which it is corrected at NCEP.
Downscaling of NWP Data, a 60-minute web lesson, addresses how model forecasts are downscaled for use by NWS forecasters in preparing high-resolution gridded forecasts. The lesson also covers capabilities and limitations of various downscaling methods (to be published in Fall 2010).
We may add more lessons to this course as new types of NWP models and methods reach forecast operations.
Course 2:
[truncated for size]
NOTE TO NWS and other NOAA EMPLOYEES: These lessons are available in the NWS Learning Center (https://doc.learn.com/noaa/nws). Please access it in that system in order to get credit.
atmo: I haven't gone through it yet, but will be. Ought to be, at least, a good refresher...and likely will be something new to me in there.
NOTE: May require a free registration to access, but is the right price and open to all.
Eastern Pacific cross over, it's going to get very interesting apparently and central America wont do so good. :(
It's looking a lot better organized as it moves westward
I just hope Matt continues the forward speed, it's in the same vicinity as another certain 'M' storm which represents the absolute worst case scenario. The rainfall wouldn't be as bad if there was no stalling, right?
i think this is what the spinoff resulted in
Thank you for the edu series link!
Looks to be a moisture surge from the ITZ and south that essentially is creating a strong tropical wave that has the potential to develop.
hey!!, you there, in the 5/10N-30/40W, of this image.... are you represented by any model ???
new stormsss
faster is better.... in forward motion of a system.
This would suck!
new storms
Which systems are you talking about?
Evening fm. I'm thinking it will be on shore in less than 24hrs. He's hauling off to the W.
I love Belize...I hit the lotto, last kid graduates...Belize is my new address.
And the ridge is still strong enough to guide Matthew's path with a southern track. Will be a mess down there this weekend. Hope the speed of the storm keeps damage and death to a minimum.
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