Sep 28, 2016

Tropical Storm Matthew

The  Tropical-disturbance-in-atlantic-invest.html that I posted on yesterday has become Tropical Storm (TS) Matthew. The satellite loop from CIMSS (below) indicates that TS Matthew continues to slowly become organized. The outflow on the north side of the storm is good and is fair to the south. The storm's proximity to the continent of South America will likely mean only a gradual intensification of the storm over the next 24 hours, nonetheless it is expected to become a minimal hurricane.

Upper air winds are favorable for a steady development based on the latest high-level wind analysis from the UW-Madison Tropical Cyclone analysis page:
The area of unfavorable shear (image below) continues to recede westward as Matthew moves to the storm as it moves in a general west or slightly north of west motion over the next 72 hours.

Thereafter, once it nears 75° W longitude model data is  forecasting Matthew to make a hard (anti-NASCAR) right-turn.
As the spatial separation increases between the storm and the coast of South America, the system is expected to intensify at a slightly faster rate; I think that during the post-72 hour period as the storm turns north there is the potential for it to undergo a period of rapid intensification. But again for now thinking/being conservative here.

At 11 PM Matthew was located approximately about 370 miles/595 kilometers SSE of San Juan, Puerto Rico or about 370 miles ENE of the Island of Curacao. Maximum winds were 65 mph with higher gusts and the storm was moving West at 15 mph.

Tropical Storm Warnings and Watches are posted for some islands in the Lesser Antilles and along the north coast of Venezuela.

Time will tell what, if any, impacts Matthew will have on the U.S. mainland. Already, the internet is abuzz with wanna be meteorologists making unfounded posts of meteorological armageddon based on long range weather models. Make sure what you view online is from a credible source - either from the NWS, NHC or a credible meteorologist! Rest assured, I'll be keeping both eyes on this system.

Sep 27, 2016

Tropical Disturbance in Atlantic - Invest 97L

A  tropical disturbance (97L) in the Atlantic Ocean located about 415 miles to the east-southeast of the island of Barbados is showing signs of becoming better organized this afternoon. Hurricane hunters are tasked to do a reconnaissance of it this afternoon.

Based on satellite wind data and minimal surface reports the system doesn't appear to have a closed cyclonic circulation at the moment. Below is a visible satellite picture of the system on the left and the satellite winds on the right.
(Visible Satellite Imagery oif 97L)

(High Level Wind Analysis over and around 97L)
(Current Divergence Analysis)
Of interest is the wind field in and around the disturbance. The wind flow is anticyclonic or diverging. Divergence increases upward motion of the air (image to right) and causes a lowering of the atmospheric pressure at the surface,

 In addition to divergence, tropical systems need warm ocean waters Sea Surface Temperatures/SST) of at least 26°C/78°F for their development or intensification. The disturbance is currently over SSTs of 28°C to 30°C (image below).

(Sea Surface Temperature analysis)
The other favorable element for potential development is for little wind shear aloft. Strong shear (of 20kts or greater) disrupts a tropical system's circulation and structure. Shear can inhibit development or even weaken a tropical system. Based on the latest wind shear analysis (image below), the shear is favorable (i.e., LOW) over 97L., but to its west the shear is strong (unfavorable).

(Current Wind shear)
However many of the forecast models are forecasting this shear to relax considerably over the next two days, that is these forecast aids are indicating little shear as 97L moves into the Eastern Caribbean Sea.

The forecast model spaghetti plots for 97L are clustered around a W to WNW heading through the end of the week. Of these models that forecast intensity of tropical systems, most if not all are forecasting 97L to become at least a tropical storm. If this did occur then 97L would be christened "Matthew".
(Forecast model ensemble tracks for 97L)
Per the NHC, "Interests in the Windward and southern Leeward Islands, Bonaire,Curacao, Aruba, and along the northern coast of South America should monitor the progress of this disturbance. Regardless of whether the system is a tropical wave or tropical cyclone, heavy rains and tropical-storm-force winds in squalls are expected to spread over the Windward Islands and portions of the southern Leeward Islands, beginning tonight and continuing through Wednesday."

Credits: First 5 images from University of Wisconsin CIMSS Tropical System web site: CIMSS