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Tropical Storm Karina Forecast Discussion Number 13
2020-09-16 04:43:02| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Tue Sep 15 2020 000 WTPZ41 KNHC 160242 TCDEP1 Tropical Storm Karina Discussion Number 13 NWS National Hurricane Center Miami FL EP162020 Issued by NWS Central Pacific Hurricane Center Honolulu HI 800 PM PDT Tue Sep 15 2020 Satellite imagery shows that Karina's outflow has improved over the past 6 hours, but persistent deep convection over the low-level center has shown some signs of warming/weakening in the last couple hours. The initial intensity for this advisory is maintained at 50 kt, primarily based on a blend of subjective Dvorak intensity estimates of 45-55 kt from SAB/TAFB/HFO. Karina is moving toward the northwest at 10 kt (310/10 kt), steered by a mid- and upper-level ridge to the northeast and north, respectively. Although some relaxation of the recent northeasterly to easterly shear is expected to continue in the short-term, gradual weakening is expected as Karina is now over sub-26C water. As Karina rounds the southwestern portion of the deep-layer ridge in about 24 hours, south to southwesterly shear is expected to increase as the cyclone moves over even cooler waters and ingests increasingly dry air. This will lead to the demise of the cyclone, and Karina is expected to degenerate to a remnant low in a couple of days, dissipating shortly thereafter. As the system weakens, it will be steered by the low-level northeasterly trade wind flow supplied by a surface high centered to the distant northwest, causing a slowing in forward speed, and a turn toward the west and southwest. The new official track forecast has changed little from the previous, and lies very close to the dynamical consensus TVCE. The new intensity forecast is little changed, and closely follows both the statistical and dynamical guidance. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 21.3N 123.0W 50 KT 60 MPH 12H 16/1200Z 22.1N 124.2W 45 KT 50 MPH 24H 17/0000Z 23.0N 125.6W 40 KT 45 MPH 36H 17/1200Z 23.4N 126.7W 35 KT 40 MPH 48H 18/0000Z 23.5N 127.8W 30 KT 35 MPH 60H 18/1200Z 23.2N 129.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 19/0000Z 22.5N 130.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 20/0000Z...DISSIPATED $$ Forecaster Birchard
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Tropical Storm Vicky Forecast Discussion Number 8
2020-09-16 04:32:20| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Sep 15 2020 269 WTNT41 KNHC 160232 TCDAT1 Tropical Storm Vicky Discussion Number 8 NWS National Hurricane Center Miami FL AL212020 1100 PM AST Tue Sep 15 2020 Vicky provided a surprise this evening, with scatterometer data showing a solid 45-kt in the northwestern quadrant of the storm. You would never guess it from the satellite images, which show a very sheared system that would at best support an 30-35 kt intensity, as indicated by the latest Dvorak estimates. The initial wind speed is set to 45 kt, higher than the last time but not really a true strengthening since conventional satellite data was a bit deceptive earlier. Despite Vicky holding its own, models are still showing the strong shear persisting, which should eventually cause weakening. The cyclone is likely to last longer than previously anticipated though with some upper-level divergence counteracting the effects of the shear, but Vicky is forecast gradually lose strength and decay in a remnant low in a couple of days, similar to the consensus guidance. The storm continues to more west-northwestward, a little to the left of previous, at 290/10. Vicky should gradually turn westward tomorrow and west-southwestward later this week as it becomes a shallower cyclone. The new forecast is quite similar to the previous one, leaning on the northern side of the well-clustered guidance envelope since Vicky is persisting as a deeper cyclone for the moment. The only small change is to add a 72-hour forecast point as the remnants could linger for a while longer. FORECAST POSITIONS AND MAX WINDS INIT 16/0300Z 21.6N 33.1W 45 KT 50 MPH 12H 16/1200Z 22.0N 34.5W 40 KT 45 MPH 24H 17/0000Z 22.3N 36.3W 35 KT 40 MPH 36H 17/1200Z 22.4N 38.0W 30 KT 35 MPH 48H 18/0000Z 22.3N 39.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 18/1200Z 22.0N 41.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 19/0000Z 21.5N 43.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 20/0000Z...DISSIPATED $$ Forecaster Blake
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Tropical Storm Karina Forecast Discussion Number 12
2020-09-15 22:59:29| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Tue Sep 15 2020 000 WTPZ41 KNHC 152059 TCDEP1 Tropical Storm Karina Discussion Number 12 NWS National Hurricane Center Miami FL EP162020 Issued by NWS Central Pacific Hurricane Center Honolulu HI 200 PM PDT Tue Sep 15 2020 Latest satellite images show little significant change in the organization of deep convection associated with Karina since the previous advisory. Although the thunderstorms are primarily limited to the southwest semicircle, they remain over the center, and outflow in the northeast semicircle appears somewhat improved in the last couple of hours. A blend of subjective Dvorak current intensity estimates of 3.0/45 kt from SAB/HFO and 3.5/55 kt from TAFB supports maintaining an initial intensity of 50 kt. Karina is crossing the 26C isotherm with an initial motion estimate of 305/10 kt, and much cooler waters lie along the forecast track. Karina is being steered by a mid- and upper-level ridge to the centered to the northeast and north respectively, and the short term forecast anticipates some relaxation of the recent northeasterly shear as Karina rounds the ridges. This should lead to slow weakening in the short term, and as south to southwesterly shear increases after about 24 hours, Karina will continue to weaken. Simulated satellite imagery based on HWRF guidance indicates the cyclone will become convection-free within about 48 hours, with dissipation following soon thereafter. As Karina weakens and becomes increasingly shallow, it will be steered by the low-level northeasterly trade wind flow supplied by a surface high centered to the distant northwest. The updated track forecast lies along the same trajectory as the previous, but is shifted slightly southward due to recent observed motion, and is near the middle of guidance envelope. The intensity forecast is essentially unchanged and closely follows trends presented by SHIPS and FSSE. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 20.7N 122.1W 50 KT 60 MPH 12H 16/0600Z 21.6N 123.3W 45 KT 50 MPH 24H 16/1800Z 22.5N 124.8W 40 KT 45 MPH 36H 17/0600Z 23.2N 126.0W 35 KT 40 MPH 48H 17/1800Z 23.5N 127.2W 30 KT 35 MPH 60H 18/0600Z 23.3N 128.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 18/1800Z 22.5N 129.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/1800Z...DISSIPATED $$ Forecaster Birchard
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Tropical Storm Teddy Forecast Discussion Number 13
2020-09-15 22:39:50| National Hurricane Center (Atlantic)
Issued at 500 PM AST Tue Sep 15 2020 000 WTNT45 KNHC 152039 TCDAT5 Tropical Storm Teddy Discussion Number 13 NWS National Hurricane Center Miami FL AL202020 500 PM AST Tue Sep 15 2020 Overall, Teddy's organization has continued to slowly improve during the past several hours. AMSR microwave imagery near 1630 UTC showed that a low- to mid-level eye feature is beginning to form. The overall convective pattern has also improved, though not enough to increase the intensity estimates at this time, which only range from 45-55 kt. The intensity is therefore held at 55 kt, but it does appear that some intensification is imminent. The AMSR image showed indications of a microwave signature commonly associated with rapid intensification in favorable environments. Low shear and warm SSTs along the forecast track are certainly conducive, though dry air continues to be a possible limiting factor. The dry air is probably the reason that dry slots continue to occasionally appear in IR imagery near the center of Teddy. Rapid intensification probabilities are not particularly high; the SHIPS RI gives a 22 percent chance of a 30-kt increase during the next 24 h while DTOPS shows a mere 1 percent chance. The rest of the intensity models forecast only modest strengthening for the next couple of days. The NHC intensity forecast is at the top of the intensity guidance for the next 48 h and slightly above all of the models after that, but I am hesitant to lower it any further at this time given the recent microwave signature and overall improvement in Teddy's structure. In contrast, Teddy's track outlook remains straightforward, and no changes of note were made to the official forecast. The tropical storm is turning gradually toward the northwest and should begin moving in that direction tonight. A ridge over the central Atlantic should then steer Teddy in that general direction for the rest of the week. The model spread is still much lower than normal, and confidence in the track forecast is fairly high. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 14.6N 47.9W 55 KT 65 MPH 12H 16/0600Z 15.5N 49.0W 65 KT 75 MPH 24H 16/1800Z 16.8N 50.2W 75 KT 85 MPH 36H 17/0600Z 18.2N 51.6W 85 KT 100 MPH 48H 17/1800Z 19.7N 53.1W 95 KT 110 MPH 60H 18/0600Z 21.0N 54.4W 100 KT 115 MPH 72H 18/1800Z 22.5N 55.8W 100 KT 115 MPH 96H 19/1800Z 25.4N 58.8W 105 KT 120 MPH 120H 20/1800Z 28.5N 61.5W 95 KT 110 MPH $$ Forecaster Zelinsky
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Hurricane Sally Forecast Discussion Number 18
2020-09-15 22:38:43| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Tue Sep 15 2020 000 WTNT44 KNHC 152038 TCDAT4 Hurricane Sally Discussion Number 18 NWS National Hurricane Center Miami FL AL192020 400 PM CDT Tue Sep 15 2020 Sally has been inching its way toward the north-central Gulf Coast today. The overall structure of the storm has remained about the same during the day with a large ragged eye in apparent in radar imagery. A NOAA P-3 aircraft that has been sampling the storm since late this morning has reported peak flight-level winds of 76 kt, and NWS Doppler radar has shown velocities of 75-80 kt at around 7000 ft. The intensity was reduced to 70 kt on the 1800 UTC intermediate advisory and remains at that value for this advisory. Radar and aircraft fixes show that Sally has been moving very slowly toward the north or 350/2 kt. The track forecast philosophy remains unchanged from the previous advisory. Sally is currently located within an area of weak steering flow between a couple of mid-level ridges to its east and west. A weak mid-level trough over the south-central United States is forecast to slide eastward over the next few days, which should cause Sally to turn north-northeastward and then northeastward over the next 24-36 hours. Sally's forward speed is expected to remain quite slow over the next 24-48 hours, but the guidance has trended slightly faster after that time. The slow forward speed is likely to result in a historical rainfall event for the north-central Gulf Coast. It may sound like a broken record, but the track guidance has again shifted eastward during the first 24-36 hours, and the NHC forecast has been adjusted accordingly. Since Sally has a large wind field, and storm surge and rainfall hazards extend far from the eye, users should not focus on the exact forecast track or specific location and timing of landfall as strong winds and bands of heavy rainfall are already affecting the Gulf Coast and will continue to do so for quite some time. The combination of upwelling and moderate westerly shear is likely to result in little change in strength prior to Sally moving onshore. Once the center of the hurricane moves onshore, rapid weakening is expected and the global models indicate that the circulation will becoming elongated along a frontal boundary in 3 to 4 days. KEY MESSAGES: 1. Historic life-threatening flash flooding due to rainfall is likely through Wednesday along and just inland of the coast from the Florida Panhandle west of the Apalachicola River to far southeastern Mississippi. Widespread moderate to major river flooding is forecast along and just inland of the central Gulf Coast. Significant flash and urban flooding, as well as widespread minor to moderate river flooding, is likely across inland portions of Mississippi and Alabama, and into Georgia and the western Carolinas this week. 2. Life-threatening storm surge is expected along portions of the coastline from Alabama to the western Florida Panhandle, including Mobile Bay. 3. Hurricane conditions are expected this evening and overnight within portions of the Hurricane Warning area along the Mississippi and Alabama coastlines and the western Florida Panhandle. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 29.5N 88.1W 70 KT 80 MPH 12H 16/0600Z 29.9N 88.1W 70 KT 80 MPH 24H 16/1800Z 30.6N 87.7W 60 KT 70 MPH...INLAND 36H 17/0600Z 31.5N 86.9W 40 KT 45 MPH...INLAND 48H 17/1800Z 32.5N 85.3W 30 KT 35 MPH...INLAND 60H 18/0600Z 33.1N 83.3W 25 KT 30 MPH...INLAND 72H 18/1800Z 33.5N 81.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 19/1800Z...DISSIPATED $$ Forecaster Brown
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