TROPICAL STORM FORMATION: GRACE
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*NOTE: In the TROPICAL STORM FORMATION line above, probabilities are for during the next 5 day period. My personal probability will be listed as either NONE, MONITORING or PROBABLE. This does not necessarily mean something will develop, but that certain forecast conditions are likely to be present, favoring development. Once NHC products become available, then the appropriate probability and percentage will be used.
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Current Storm Total for 2015:
TOTAL STORMS: 7
INTENSE HURRICANES: 1
U.S. LANDFALLS: 2
StormW’s Seasonal Forecast:
TOTAL STORMS: 8
INTENSE HURRICANES: 1
Good day everyone!
Tropical Storm GRACE continues to move toward the west, with estimated sustained winds of 45 mph. As of the 5:00 a.m. advisory, the following was available on Tropical Storm GRACE:
11:00 AM AST Sun Sep 6
Location: 12.9°N 29.9°W
Moving: W at 14 mph
Min pressure: 1004 mb/29.65 in
Max sustained: 45 mph
Based on satellite loop images, and current steering layer mean, GRACE is moving toward the west, on the southern periphery of the subtropical ridge. Based on my analysis of the current steering layers forecast maps, I concur with the NHC forecast in that GRACE should continue on the west, to just north of west track during the next 72-96 hours. Thereafter, a weakness/break in the subtropical ridge is forecast near 65W, which would allow GRACE to ensue a more WNW track. However, past day 5, forecast steering suggests the ridge to begin to fill and expand more toward the west, at which time there could be a bend back toward the left. This will remain to be seen, as this is stepping beyond the bounds of reliable steering accuracy, however would coincide with a weaker system moving more toward the west, and is reflected in the 12Z Dynamic Model guidance TVCN track.
ATCF 12Z DYNAMIC MODEL GUIDANCE
GRACE continues to have convection wax and wane near her center, which would tend to lend credence to still some dry air ingestion. Close up water vapor loop imagery tends to verify this, as well as the presence of a stratocumlus cloud deck to her north, indicating stable dry air.
Satellite loop imagery tends to show a fairly tight core, and some slight banding features becoming a little more prominent over the last few hours.
The most recent available shear map indicates GRACE to be on the western periphery of an upper level anticyclone. The current flow is still providing some outflow aloft, with the strongest outflow channel being located on the southern portion of the storm.
The current wind shear forecast continues to call for upper level winds to improve, with the upper level anticyclone developing over GRACE, and maintaining itself for approximately the next 48 – 60 hours. Zonal shear, based on the forecast, should remain low up until that point. Thereafter, should GRACE remain on track, SWLY shear is forecast to begin to develop. This should begin to weaken GRACE. The SWLY shear is forecast to remain in place well past the forecast period, which would indicate a decent probability of GRACE’s demise later in the period. Based on this shear forecast, I concur with the current NHC intensity forecast. I believe the slow strengthening will be attributed more to drier air, vice upper level winds.
INIT 06/1500Z 12.9N 29.9W 40 KT 45 MPH
12H 07/0000Z 13.0N 32.0W 45 KT 50 MPH
24H 07/1200Z 13.3N 34.7W 50 KT 60 MPH
36H 08/0000Z 13.6N 37.4W 55 KT 65 MPH
48H 08/1200Z 13.8N 40.1W 55 KT 65 MPH
72H 09/1200Z 14.3N 45.3W 50 KT 60 MPH
96H 10/1200Z 15.0N 50.5W 40 KT 45 MPH
120H 11/1200Z 15.5N 55.5W 35 KT 40 MPH
I will continue to monitor GRACE for any significant changes.
Elsewhere, I will be monitoring a tropical wave exiting the African coast, south of where GRACE entered the Atlantic. This feature currently has an upper level anticyclone over it, and upper level winds are forecast to remain somewhat favorable for the next 3 days. We’ll have to see what happens as this hits the ocean, as there doesn’t appear to be as much convection or moisture with it.
Elsewhere, Tropical Storm formation is not expected during the next 5-7 days.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /
SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS