TROPICAL CYCLONE FORMATION: T.S. KARL / INVEST 96L (90%)
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(T. F. “Storm” Walsh III)
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CURRENT 2016 ATLANTIC TROPICAL CYCLONE TOTALS:
TOTAL STORMS: 11
MAJOR HURRICANES: 1
StormW’s Seasonal Hurricane Forecast:
TOTAL STORMS: 13-15
INTENSE HURRICANES: 3-4
Good day everyone!
Tropical Depression Julia was downgraded to a remnant low, and the NHC issued it’s last advisory early this morning. However, based on analysis of surface forecast maps, 500 mb anomaly maps, and given the warm Gulfstream and forecast steering, the remnant low could possibly become somewhat of a small Nor’easter due to some baroclinic forcing from the approaching front, possibly riding along or near the coastal Carolina/ Va area. This may bring onshore winds along the coast over the next 72 hours, along with rainfall. The current run of the STORMSURF Wavewatch model suggests sustained wind away from the center in the range of 15 – 20 kts IVO OBX by late tonight/early Tue., with winds 25 – 30 kts near the mouth of the Chesapeake Bay by Wed. Given the small wind radius projected, there could be some minor coastal flooding in some areas, however based on the model output at this time, it may not be very serious…but keep in mind, conditions can and do change rapidly. One thing did notice in analysis, is upper level winds are forecast to be favorable, indicating an upper level anticyclone over that area for a breif period. Residents along the OBX and Tidewater vicinity may wish to monitor this by following local NWS statements.
Elsewhere, Tropical Storm Karl remains disorganized, as it moves to the west this afternoon. As of the 11:00 a.m. advisory, the following information was available on Karl:
11:00 AM AST Mon Sep 19
Location: 18.6°N 48.3°W
Moving: W at 13 mph
Min pressure: 1006 mb / 29.71 in
Max sustained: 40 mph
Karl has changed little in satellite presentation, with the convection being displace to the NE of the LLC due to 15 – 20 knots of SWLY wind shear. Analysis of water vapor imagery and PWAT analysis indicates mid level dry air is also affecting the storm, mainly on the west and SW portion.
Based on my analysis of the current wind shear forecast from both the GFS and ECMWF, the upper level pattern is forecast to slowly improve in about 24-30 hours, and continue to improve through days to days 5-6 in the forecast period, with the development of an upper level anticyclone projected to be over the center of Karl. Analysis of 700 – 500 MB RH maps indicates the mid levels of the atmosphere could see an increase in moisture (RH) beginning in about 72-96 hours. Based on current forecast track thinking, Karl will also be passing over higher SST’s, and somewhat higher OHC in about 60-72 hours. Based on this analysis, I concur with the NHC intensity forecast, in that only slight strengthening may occur during the next 48 hours, with a more steady strengthening from 72-120 hours. In fact, looking at the items in my analysis, should everything come to fruition, We should begin to see some improvement in structure as Karl passes 60W, with the more steady intensification once he reaches 70W. Karl is still forecast to become a category ONE hurricane in 96 hours, and I concur with this scenario at the moment, based on all of the information I have to work with.
Karl continues to move toward the west, and I expect this motion to continue for the next 24hours. Beyond this point, the cyclone should be approaching a weakness in the subtropical ridge, which has been projected by both the GFS and ECMWF for the past 2 days, and should turn toward the WNW to NW. Based on this analysis, I concur somewhat with the NHC official track, which is close to the consensus modeling. On this forecast track, Karl may pass east of Bermuda in about 6-7 days. However, should Karl remain disorganized and a weaker system a little longer than forecast, Karl could quite possibly travel a little further toward the W or WNW, which could put Bermuda in the risk of a direct hit. One other scenario, which is becoming slim with each model run depicting the large break in the ridge, and a strong 500 mb trof digging aggressively south, is Karl could remain weak, and stall as he approaches the weakness. As of my complete analysis at this time, I am not seeing this as a viable scenario at the moment.
Residents of the Island of Bermuda, should monitor the progress of Karl closely during the next 4-5 days.
Elsewhere, INVEST 96L has become somewhat better organized, and is located SW of the Cabo Verde Islands. As of the 12Z ATCF BTK product issuance, the following was available on INVEST 96L.
8:00 AM AST Mon Sep 19
Location: 13.2°N 27.0°W
Moving: W at 11 mph
Min pressure: 1007 mb / 29.74 in
Max sustained: 35 mph
The disturbance has become better organized based on satellite loop imagery. Upper level winds are conducive for further slow organization, with an established upper level anticyclone over the system. IF this disturbance continues to organize today, I believe it could become a Tropical Depression sometime this evening. Based on my analysis of the current wind shear forecast, 96L should remain in a favorable environment for at least the next 72 hours, as the upper level anticyclone remains established over the system. Shortly thereafter, based on forecast position, upper level wind are forecast to become less conducive, and current intensity guidance indicates weakening of the system beginning by day 3-4 in the period. The intensity models do bring this to Tropical Storm strength, and by 6o hours, max it out as a mid grade Tropical Storm. This however is subject to change, should the INVEST become organized quicker.
Based on the ATCF product, the INVEST is moving to the west. I expect this motion to continue for most of today. Based on analysis of the forecast steering maps, indications are that the disturbance should begin to move toward the WNW, then NW due to the influence of break in the eastern periphery of the subtropical ridge. Looking at dynamic guidance this morning, the guidance already suggests a WNW motion. However, I am inclined to disagree with this at the moment, as satellite loop imagery continues to indicate a westward movement, with cloud motion in the lower level showing the ridge nosing westward. Based on this, I believe the model guidance may shift toward the left. I do agree with the turn however, but feel it will be briefly delayed.
Elsewhere, analysis of both the GFS and ECMWF suggests another system off the African coast in 9-10 days, along with a possible situational development around the vicinity of the Bahamas area (ECMWF) or possibly GOMEX (GFS). Based on the long standing fact of the ECMWF being the more accurate model, it appears that as Karl passes toward Bermuda, some vorticity at the 850 mb level may break toward the Bahamas. In this time period in the 6-10 day forecast period, around day 8, a ridge is forecast to be over the SE U.S., causing pressure height falls to its south. This could possibly allow for a close in development situation. I will be monitoring both of these situations as the time draws near.
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