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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23Sep 12amGMT - - 13.1n72.0w - - 30knots - - 1007mb - - NHC-ATCF *12.9n
23Sep 06amGMT - - 13.4n73.5w - - 30knots - - 1008mb - - NHC-ATCF *13.2n
23Sep 12pmGMT - - 13.6n74.8w - - 30knots - - 1007mb - - NHC-ATCF *13.5n
Invest95L becomes TropicalDepression15
23Sep 06pmGMT - - 13.9n76.2w - - 35mph - - -1007mb - - NHC.Adv.#1
TD.15 becomes Tropical StormMathew
23Sep 09pmGMT - - 14.0n76.9w - - 40mph - - - 1006mb - - #2
24Sep 12amGMT - - 14.2n77.7w - - 40mph - - - 1005mb - - #2A
30knots=~34.5mph
* Before NHC reevaluated&altered the numbers
Copy&paste 13.1n72.0w, 13.4n73.5w-13.6n74.8w, 13.6n74.8w-13.9n76.2w, 13.9n76.2w-14.0n76.9w, 14.0n76.9w-14.2n77.7w, pnd, nbw, vqs, trb, 14.2n77.7w-15.75n84.25w into the GreatCircleMapper for a look at the last 18^hours.
^ The westernmost line-segment is the straightline projection using the heading
averaged over the 3hours spanning the last two reported positions
The following 2 line-segments indivdually span 3hours between dots.
The 2 easternmost line-segments individually span 6hours between dots.
The unconnected dot is separated by 6hours.
Link?
its not heading for TX its heading for FL
Without food....
he has already started a near WNW movement, as he's beginning to rapidly intensify imo..
I suspect it could become a hurricane tonight
Mathew is spinning up like he wants to be a serious 'cane soon, and the silly models are pointing in all directions. Trofs and timing. But people are more interested in reporting each other and picking fights. Sigh!
I think things will be much clearer as to track and potential intensity in the morning as a little time will resolve some uncertainties and give us a better fix.
:)
From what I can tell it will be from moisture that will pop up around Haiti.
18z HWRF
So does Steve G. on WFLA!
HWRF may be on to something..
the thing is already it's developing SIGNIFICANT hot towers.. that already indicates the circulation is deepening, and will likely deepen rapidly tonight.. similar to KARL but karl hit land before it could really erupt near the yucatan.. the same could be said about alex..
the thing is matthew has space this time.. and developed a tight closed low throughout the day.. this will allow him to explode to night.. and it's already beginning on satellite..
Like I said it should be a much stronger system that forecasted, as the conditions are favorable for some rapid development at the moment.. a weak anticyclone seems to have also formed over Matthew on satellite..
so.. yea.. I again I suspect it could become a hurricane rather quickly before the sun comes up..
Depends on which model you follow. The latest runs (18z) are, through the FSU website, only available by GFS and EWRF.
The Oriente region of Cuba, the western most province, may get hit IF the EWRF model is correct. It's still too far out to know. The NHC may lose accuracy points for the year due to this system. Very complicated atmospheric situation here.
The 18 UTC HWRF has bad feedback issues around the vortex-following grid boundaries that are propagating though the domain.
What does this mean for HWRF track and intensity? Probably indeterminable, but I'll not be looking too closely at HWRF's results, I think. Intensity is prolly especially bad...
Same time for GFDL:
I wonder if they shouldn't try one-way feedback in HWRF...assuming they are doing two-way.
Weatherguy said the ULL is currently ventilating Matthew. It's actually helping it to develop further. However, he did voice the possibility of the ULL nearing closer to Matt and therefore impairing development.
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