TROPICAL CYCLONE FORMATION: HURRICANE GASTON / T.D. 8 / T.D 9
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 7
INTENSE HURRICANES: 1
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good evening everyone!
SPECIAL UPDATE ISSUED 6:00 P.M.
Information contained in the 5:00 p.m. advisories from the NHC regarding Tropical Depression EIGHT and Tropical depression NINE indicate that a Tropical Storm WARNING has been issued for portions of the North Carolina coast, regarding Tropical Depression EIGHT. The following is the discussion link and public advisory link
LOCAL STATEMENT FROM MOREHEAD CITY NC NWS
Regarding Tropical Depression NINE, the following are links to the public advisory and forecast discussions:
There are currently no watches or warnings posted, however, the 5:00 p.m. advisory included the following paragraph:
Given the current forecast, a tropical storm or hurricane watch may be required for a portion of the Florida Gulf coast as early as tomorrow morning.
The following was the wind speed probability percentage posted in the 5:00 p.m. advisory for the probability of areas that may experience TS force winds of 39 mph.
I will have another update tomorrow.
Briefly on Hurricane GASTON…the hurricane is in weak steering at the moment, and is drifting slowly to the north. There is no real change in the forecast thinking, in that GASTON should begin to move toward the ENE as a ridge becomes established south of the hurricane. This should occur in about 24-30 hours, allowing the hurricane to move slowly to the ENE at first, then accelerating thereafter. GASTON should not be a threat for the U.S.
Tropical Depression EIGHT continues to remain weak and disorganized. As of the 11:00 a.m. EDT advisory from the NHC, the following was available on T.D. EIGHT:
1:00 AM EDT Mon Aug 29
Location: 33.2°N 73.5°W
Moving: NW at 7 mph
Min pressure: 1011 mb / 29.85 in
Max sustained: 35 mph
Satellite loop imagery indicates the LLC to be naked and to the SE of the convection. This is currently being caused by some SELY wind shear over the system. It is noted however that a burst of convection has recently appeared on the NW edge of the exposed center. This may be a sign that wind shear may be beginning to relax, which is forecast over the next 24 hours, for a breif period. This may allow for some organization and slight strengthening to occur, and is reflected in the NHC intensity guidance. Based on this, T.D. EIGHT could become a tropical storm during the next 24-36 hours. Based on the intensity guidance from the SHIP, DSHP, and LGEM models, I concur with the NHC intensity scheme.
NHC INTENSITY FORECAST
INIT 29/1500Z 33.2N 73.5W 30 KT 35 MPH
12H 30/0000Z 33.8N 74.3W 30 KT 35 MPH
24H 30/1200Z 34.4N 75.0W 35 KT 40 MPH
36H 31/0000Z 35.1N 75.0W 35 KT 40 MPH
48H 31/1200Z 36.2N 73.5W 40 KT 45 MPH
72H 01/1200Z 39.0N 68.0W 45 KT 50 MPH
There is no change in thinking as far as forecast track, as due to a forecast break in the ridge, along with a mid latitude shortwave trof forecast to dip down, this should steer the depression away from the OBX area, and re-curve it to the NE in couple days. Based on analysis of forecast steering maps, and dynamic guidance being tightly clustered, I concur with the NHC forecast track.
A Tropical Storm WATCH is in effect for a portion of the OBX:
SUMMARY OF WATCHES AND WARNINGS IN EFFECT AND HAZARDS ISSUED BY THE NHC:
A Tropical Storm Watch is in effect for… * The coast of North Carolina from Cape Lookout to Oregon Inlet
A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, in this case within 36 hours.
Interests elsewhere along the Outer Banks of North Carolina should monitor the progress of the depression. Additional watches or warnings may be required later today.
For storm information specific to your area, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office.
HAZARDS AFFECTING LAND
WIND: Tropical storm conditions are possible within the watch area by Tuesday afternoon.
RAINFALL…The depression is expected to produce total rain accumulations of 1 to 3 inches with isolated maximum amounts of 5 inches over far eastern North Carolina, including the Outer Banks.
The following link is from the local NWS statement issued from the NWS in Morehead City, NC.
NWS LOCAL STATEMENT MOREHAEAD CITY NC
Residents of the OBX should monitor NOAA Weather Radio and local NWS Statements and warnings regarding this system. Given the onshore flow as the system approaches close to the coast, residents should remain of the water and away from the beaches due to rip currents and the probability of minor coastal flooding at the time of high tide.
Elsewhere, Tropical Depression NINE continues to be disorganized, and was located north of the western tip of Cuba. At 11:00 a.m. the following information was available on T.D NINE from the NHC advisory:
11:00 AM EDT Mon Aug 29
Location: 23.6°N 84.3°W
Moving: W at 7 mph
Min pressure: 1007 mb / 29.74 in
Max sustained: 35 mph
Satellite loop imagery indicates convection at the mid levels becoming better organized, with the convection beginning to become closer to the LLC. In fact, the final frame of the loop shows a small burst of convection just at the SE edge of the LLC. The depression is still being plagued by 30 kts of NWLY shear, due to the close proximity of an upper level low centered off the GA/SC coastal region. The current wind shear forecast indicates shear may relax over the next 24 hours, which would allow for thunderstorm activity to grow closer to the center. Both the GFS and ECMWF still call for an upper level anticyclone to develop over, or near the center of the depression in about 42-48 hours. The upper level wind product from CIMSS did indicate an outflow pattern to the east and south of the system was present.
Having analyzed the NHC forecast discussion, I am a little perplexed as to why strengthening and intensity is forecast as such, if the upper feature is directly overhead. The NHC mentions that by 72 hours, the flow aloft becomes more baroclinic with westerlies over north FL. My thought is, that TD NINE remains close to the western edge of the upper level anticyclone, with just enough of a diffluent flow to allow for some slight to moderate divergence, vice being in an optimal 200 mb pattern. The NHC also mentioned dry air may hinder this slightly, in the previous advisory. I believe the upper pattern will have more of an influence on strengthening, as TD 9 is in an environment with high precipitable water values.
If the shear forecast ever pans out, I believe the 36-48 hour frame in the forecast period will be where we see a little quicker organization and strengthening, as compared tot he current situation. I am not inferring Rapid Intensification, but a more steady organization within that specified time frame. With the lack of an optimal upper level pattern, and much lower OHC in which this will be passing over…R.I. is not an issue, and these forecast items may be what keeps the depression within the intensity scheme. Based on analysis of these parameters, a I am inclined to concur with the NHC intensity forecast at the moment. Depending on how well the models are handling the upper level pattern, as far as shear, and whether this begins to organize at a decent rate once it gets further from Cuba, I will hold the slim possibility of a minimal CAT 1 hurricane, which is currently forecast by the SHIPS and DSHP models in 72 hours. It is noted however, that these models have been slowly decreasing their intensity over the past few runs, so for official purposes, this office will remain with the NHC intensity scheme.
NHC INTENSITY FORECAST
INIT 29/1500Z 23.6N 84.3W 30 KT 35 MPH
12H 30/0000Z 23.9N 85.3W 35 KT 40 MPH
24H 30/1200Z 24.4N 86.4W 40 KT 45 MPH
36H 31/0000Z 25.0N 87.0W 45 KT 50 MPH
48H 31/1200Z 26.1N 86.7W 50 KT 60 MPH
72H 01/1200Z 28.6N 83.8W 55 KT 65 MPH
96H 02/1200Z 31.5N 79.0W 50 KT 60 MPH
120H 03/1200Z 34.0N 71.5W 50 KT 60 MPH
The depression is currently moving slowly to the west, however based on the current steering pattern, should begin to move more to the WNW later today.
Based on my analysis of the current forecast steering layers maps, I expect this motion to continue for the next 24-30 hours, before a slow turn to the north begins to occur. I know some folks have been questioning this turn, regarding on how sharp it seems. Based on the forecast steering maps at the moment, here’s what happens…During the time frame mentioned, in about 36 hours from 12Z, the ridge seen in current steering, which has been over the Mid Atlantic states, begins to retrograde toward the west, and eventually collapses. This is going to create a weakness along the eastern seaboard. Combined with this, will be the resultant flow of the ridge that builds and becomes centered near 25N;62W, creating a SW to NE flow. Based on current timing of these features, this explains the turn of TD NINE. The dynamic guidance models, the global models, especially the ECMWF Ensemble members are in agreement of this turn, which is reflected in the 12Z dynamic guidance. Based on this analysis, I concur with the NHC forecast track, albeit fluctuations can occur, which would determine whether or not this makes landfall a little further north or south of the projected track.
There are no watches or warnings posted as of yet, and given the wide error cone, residents along the Florida west coast from Apalachicola to the Tampa Bay area should monitor the progress of this system closely.
As the system makes its turn and begins to track toward the FL. coast, tropical storm force conditions could affect a good portion of the FL. west coast, mainly near the center and right of track. Heavy rainfall will affect south Florida, and could affect much of the west coast of the peninsula as the system approaches landfall. The following are forecast rainfall totals for the next 3 and 5 day period
WPC 72 HOUR RAINFALL TOTALS
WPC 5 DAY QPF
This rainfall is likely to cause flooding problems in low lying areas, and areas prone to flooding during normal thunderstorm activity. As the system approaches the coast, some coastal flooding and beach erosion may occur during periods of high tide, if this becomes a tropical storm.
Residents along the wets cost of Florida should monition NOAA Weather Radio, and local NWS statements regarding this system. The following map is linked for current information regarding your area. Click on it for your area of interest.
Elsewhere, another tropical waves is about to enter the E. Atlantic off the African coast. Upper level winds are currently somewhat favorable for slow development, and analysis of the shear forecast indicates an upper level anticyclone to develop near or over the wave, and be maintained for at least the next 5 days, and is forecast to have high TPW totals associated with it. If these conditions pan out, it may have a good chance at steady development. Forecast steering indicates this may make a westerly track for about 5-6 days, and be just north of the islands. I will keep an eye on this, as we know how steering can change. NHC designates a MEDIUM (50%) probability of cyclone development over the next 5 days
I intend to have another update tomorrow, and Wed….time unknown.
Have a blessed day!
T. F. “STORM” WALSH III
GMCS, USCG (ret)
METEOROLOGIST / HURRICANE SPECIALIST /SEVERE WEATHER SPECIALIST
MEMBER WEST CENTRAL FLORIDA AMS