Tropical Storm Matthew Develops, Long Term Forecast Uncertain

Tropical Storm Matthew Develops, Long Term Forecast Uncertain

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Tropical Storm Matthew Develops, Long Term Forecast Uncertain

Tropical Storm Matthew has formed near the Windward Islands moving generally westward at around 18 knots. A hurricane hunter plane estimated surface winds of 50 knots, and there’s ...

Tropical Storm Matthew has formed near the Windward Islands moving generally westward at around 18 knots. A hurricane hunter plane estimated surface winds of 50 knots, and there’s little reason to doubt that estimation. As such, the NHC has initiated advisories on the storm at 60 mph.

Note: Many Caribbean islands are in the path of this potentially very dangerous storm. This article focuses on CONUS impact. Those in the path outside of the United States should still pay attention!

From the NHC:

SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

 A TROPICAL STORM WARNING IS IN EFFECT FOR…* GUADELOUPE AND MARTINIQUE* ST. LUCIA* DOMINICA, BARBADOS, ST. VINCENT, AND THE GRENADINE ISLANDSINTERESTS IN BONAIRE…CURACAO…ARUBA…AND ELSEWHERE IN THELESSER ANTILLES SHOULD MONITOR THE PROGRESS OF MATTHEW.
TROPICAL STORM CENTER LOCATED NEAR 13.4N  60.7W AT 28/1500Z
POSITION ACCURATE WITHIN  30 NM PRESENT MOVEMENT TOWARD THE WEST OR 275 DEGREES AT  18 KT

While the storm is producing somewhat high winds at 60 mph, it’s important to remember that this is in large part due to interaction with a strong high pressure system to the north. Matthew is still in its developmental stages despite such high winds, and could be slow to develop in the short term.

So, as usual, the question is “Where’s it going, and how strong will it be?”

The computer guidance is in fairly good agreement on track through the short term, so we will skip over that part. Wxchasing.com is, at the moment, in near lock-step with the forecast from the NHC through the near term, which we believe to be a very good one given current information. The divergence in computer guidance in the short term (inside of 3-4 days) is largely along-track. Meaning, most guidance agrees on the track but disagrees on how quickly the storm gets there.  This timing difference becomes very important later on as it will determine just how far west the storm can get, and subsequently what sort of impacts to land we might see.

Below, the Euro, CMC, and GFS illustrate how dramatically different the situation can unfold beyond 4-5 days depending on the depth of the troughing that is creating a weakness for the storm o move north into, how strong the storm is (a stronger storm typically can “feel” a trough more as it already has a tendency to move to the right of the steered trajectory due to the Beta effect, the conservation of vorticity)

ecmwf_z500_mslp_us_11
gem_z500_mslp_us_41gfs_z500_mslp_us_41
The spread among models is quite large in the extended range. One way to judge confidence in a forecast is to examine an ensemble of modeling. The GFS and Euro produce an ensemble of modeling where a whole pile of slightly-less-precise than the operational runs are created. As you can see below, the euro and gfs are vastly different, but more than that the euro shows a huge range of solutions possible and the gfs has as many solutions indicating a landfall on the east coast as it does a solution entirely out to sea. A very complex forecast regarding track.
ecmwf-ens_mslpa_us_11 gfs-ens_mslpa_us_41

Based on the latest trends, our forecast is for a slightly slower storm movement than is indicated by the NHC. Below, you can see where our forecast (red dots) begin to slightly diverge from the NHC (black dots) beginning Monday morning.  At that point we believe the storm will be moving more slowly, and perhaps just west of the current NHC expectation.

forecast-track-9-28-16-am

Regarding intensity, most guidance eventually brings Matthew up to hurricane intensity. The latest guidance of the MJO (Madden-Julian Oscillation) indicates favorable conditions for intensification with general upward motion over the Atlantic Basin as well.

ncpe_phase_21m_small ecmf_phase_51m_small

At this time, we have no reason to disagree with the forecast from the NHC, as below :
INIT  28/1500Z 50 KT  60 MPH 12H  29/0000Z 50 KT  60 MPH 24H  29/1200Z 55 KT  65 MPH 36H  30/0000Z 60 KT  70 MPH 48H  30/1200Z 65 KT  75 MPH 72H  01/1200Z 70 KT  80 MPH 96H  02/1200Z 80 KT  90 MPH120H  03/1200Z 90 KT 105 MPH

There are a few stronger outliers at the moment, with the HWRF and GFDL models indicating rapid intensification in the Caribbean. For now, we don’t anticipate such rapid development but interests in the area should prepare for the possibility of a major hurricane.

gfdl-p_mslp_wind_97l_22
hwrf-p_mslp_wind_97l_43
(938 mb before land interaction)

Beyond 120 hours, land interaction should halt strengthening and perhaps induce some temporary weakening before the storm gets going again as it emerges into the Bahamas.

This storm will likely have a few surprises along the way, so even if you aren’t in the expected path, if you are along the northern Gulf Coast, Florida, or the East Coast, this storm deserves your attention. We will be updating you here as changes in forecast thinking occur.

Meteorologist Logan Poole
Wxchasing.com