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Hurricane Florence Forecast Discussion Number 43
2018-09-10 04:48:51| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 09 2018 663 WTNT41 KNHC 100248 TCDAT1 Hurricane Florence Discussion Number 43 NWS National Hurricane Center Miami FL AL062018 1100 PM AST Sun Sep 09 2018 Florence's satellite appearance has continued to improve quite markedly since the previous advisory. An eye was evident in GOES-16 high-resolution infrared imagery and other channels between 2300-0000 UTC, but it became cloud covered immediately thereafter due to a strong burst of deep convection in the southern and eastern eyewall where cloud tops colder than -80C and an abundance of lightning activity was observed. Since that time, the CDO has expanded and become more circular, outflow has increased and become more symmetrical, and an eye has begun to re-appear. The initial intensity has been increased to 80 kt for this advisory based on a subjective Dvorak intensity estimate of T4.5/77 kt from SAB and NHC objective intensity estimates ranging from 77 kt to 87 kt. The initial motion estimate is 280/06 kt. Once again, there is no significant change to the previous forecast track or synoptic reasoning. The models appear to be getting better dialed in on both the location and strength of the developing blocking ridge in the vicinity of Bermuda during the next 4 days as the mid-latitude flow amplifies across the CONUS and the northwestern Atlantic. In fact, the global models are now in very good agreement on forecasting Florence's upper-level mass outflow being deposited to the north and east of the hurricane, which will act to further strengthen the blocking ridge and help to drive the hurricane northwestward toward the southeastern U.S. coastal region. The new NHC model guidance is even more tightly packed about the previous forecast track, with less than a 90 n mi cross-track spread at 72 h and less than 120 n mi spread at 96 h, just prior to expected landfall. Therefore, the new official advisory track is essentially just an update and extension of the previous forecast, and lies between the nearly juxtaposed HCCA and FSSE corrected consensus track models. Now that Florence has developed an inner-core ring of deep convection, which has insulated the eye from intrusions of dry air, rapid intensification appears likely to begin soon and continue for the next 36 hours or so due to the expected very low vertical wind shear conditions, dual outflow jet pattern that will be developing, and very warm SSTs of 29-29.5 deg C beneath the hurricane. The most favorable combination of the aforementioned factors will occur in about 48 h, and that's when Florence is likely to achieve its maximum intensity. After 72 hours, the wind shear is expected to increase to around 10-15 kt from the south or southwest, and the dual outflow pattern is forecast to change to only a single poleward outflow pattern. This slight degradation in the upper-level environment, along with slightly cooler SSTs, is expected to result in a gradual weakening of the powerful cyclone. However, Florence is still forecast to be near category-4 strength when the dangerous hurricane makes landfall. The official intensity forecast is an average of the intensity forecast from the corrected consensus models HCCA and FSSE, with the latter explicitly forecasting a peak intensity of 134 kt in 72 hours. It is also worth noting that the model guidance is also significantly increasing the size of Florence's wind field over the next few days, and the official forecast reflects this trend. The NOAA G-IV jet will conduct another synoptic surveillance mission early Monday morning in support of the 1200 UTC model cycle, and these flights will continue through Tuesday. In addition, upper-air stations across portions of the central and eastern U.S. are conducting special 0600 UTC and 1800 UTC radiosonde launches to collect extra data for the numerical models. Hopefully these data will help improve the track and intensity forecasts. Key Messages: 1. There is an increasing risk of two life-threatening impacts from Florence: storm surge at the coast and freshwater flooding from a prolonged heavy rainfall event inland. While it is too soon to determine the exact timing, location, and magnitude of these impacts, interests at the coast and inland from South Carolina into the mid-Atlantic region should closely monitor the progress of Florence, ensure they have their hurricane plan in place, and follow any advice given by local officials. 2. Large swells affecting Bermuda and portions of the U.S. East Coast will continue this week. These swells will result in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 24.6N 57.7W 80 KT 90 MPH 12H 10/1200Z 24.9N 59.1W 90 KT 105 MPH 24H 11/0000Z 25.6N 61.5W 105 KT 120 MPH 36H 11/1200Z 26.5N 64.4W 120 KT 140 MPH 48H 12/0000Z 27.8N 67.6W 130 KT 150 MPH 72H 13/0000Z 31.2N 73.6W 130 KT 150 MPH 96H 14/0000Z 34.0N 77.5W 120 KT 140 MPH 120H 15/0000Z 35.2N 79.0W 55 KT 65 MPH...INLAND $$ Forecaster Stewart
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Hurricane Helene Forecast Discussion Number 11
2018-09-10 04:37:50| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sun Sep 09 2018 951 WTNT43 KNHC 100237 TCDAT3 Hurricane Helene Discussion Number 11 NWS National Hurricane Center Miami FL AL082018 1100 PM AST Sun Sep 09 2018 Satellite images indicate that Helene continues to strengthen. During the past several hours, a large band of deep convection has completely wrapped around the center resulting in the formation of a large ragged eye. Although there are well-defined outer bands in the southern portion of the circulation, there are a few dry slots just beyond the inner core. The latest Dvorak classifications have increased to 4.5/77 kt from both TAFB and SAB, and therefore, the initial intensity is adjusted upward to 75 kt. Helene is currently in a low wind shear environment and over fairly warm 27-28 deg C SSTs. These conditions are expected to prevail for another 24-36 hours, so additional strengthening seems likely during that period. Beyond that time, however, the environment is expected to gradually become less favorable for Helene with south-southwesterly shear increasing, mid-level humidities falling, and SSTs lowering along the future path. All of these conditions suggest a steady weakening trend beginning in a couple of days, and the NHC intensity forecast follows the trend in the latest model guidance. The hurricane continues to pull away from the Cabo Verde Islands, and the initial motion estimate is 285/11 kt. A continued west-northwest motion at about the same forward speed is expected for about two days while a mid-level ridge remains the primary steering feature. After that time, a significant weakness in the ridge, caused by a cut off deep-layer low pressure system, should promote a northward turn with a gradual increase in forward speed. The models are in relatively good agreement on this scenario, but they differ on when and where Helene makes the turn. The NHC track forecast is adjusted a little to the east at the latter forecast times, but it still favors the left side of the guidance envelope to be near the HCCA model. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 13.9N 27.2W 75 KT 85 MPH 12H 10/1200Z 14.4N 29.2W 85 KT 100 MPH 24H 11/0000Z 15.1N 31.8W 90 KT 105 MPH 36H 11/1200Z 15.7N 34.2W 90 KT 105 MPH 48H 12/0000Z 16.4N 36.1W 85 KT 100 MPH 72H 13/0000Z 19.0N 38.7W 70 KT 80 MPH 96H 14/0000Z 23.5N 40.5W 60 KT 70 MPH 120H 15/0000Z 29.6N 41.2W 55 KT 65 MPH $$ Forecaster Cangialosi
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Tropical Storm Paul Forecast Discussion Number 7
2018-09-10 04:31:17| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Sun Sep 09 2018 942 WTPZ43 KNHC 100231 TCDEP3 Tropical Storm Paul Discussion Number 7 NWS National Hurricane Center Miami FL EP182018 800 PM PDT Sun Sep 09 2018 Paul is looking very ragged this evening. The low-level center has become completely exposed, with the nearest deep convection displaced about 70 n mi to its southwest. The intensity has been held at 40 kt, deferring to earlier ASCAT data which showed a wide swath of 35-40 kt winds. Given the structure of Paul, any intensification seems very unlikely, so gradual weakening is now forecast through the end of the period. By day 4, a combination of cold SSTs and dry, stable air should cause the cyclone to become a remnant low. The new NHC forecast shows faster weakening than before, and is now closer to the intensity consensus through 120 h. The low-level swirl that makes up most of Paul has wobbled a bit this evening, but a longer-term motion estimate is still northwestward, or 320/9 kt. The global models are in good agreement that Paul will continue northwestward for another day or so, before gradually turning westward as it weakens and eventually becomes a remnant low. No significant changes were made to the track forecast, which remains very near the multi-model consensus throughout the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 10/0300Z 19.4N 119.4W 40 KT 45 MPH 12H 10/1200Z 20.4N 120.4W 40 KT 45 MPH 24H 11/0000Z 21.2N 121.8W 35 KT 40 MPH 36H 11/1200Z 21.9N 123.6W 35 KT 40 MPH 48H 12/0000Z 22.4N 125.4W 35 KT 40 MPH 72H 13/0000Z 23.1N 128.3W 30 KT 35 MPH 96H 14/0000Z 23.5N 130.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 15/0000Z 23.5N 132.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Zelinsky
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Hurricane Florence Forecast Discussion Number 42
2018-09-09 22:53:18| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Sep 09 2018 270 WTNT41 KNHC 092053 TCDAT1 Hurricane Florence Discussion Number 42 NWS National Hurricane Center Miami FL AL062018 500 PM AST Sun Sep 09 2018 The last reconnaissance fix indicated that the pressure had fallen to about 978 mb with Florence, a drop of about 6 mb in 4 hours, with uncontaminated SFMR winds of about 70 kt. Since then, the satellite presentation has continued to improve, with intensifying deep convection near the center. Thus the wind speed is set to 75 kt on this advisory. Radar data from the NOAA Hurricane Hunter indicated that there were still a few breaks in the eyewall, possibly allowing some dry air to mix into the core. This structure has potentially kept Florence from intensifying rapidly so far. It is likely, however, that the eyewall will close soon with low environmental shear present, resulting in a faster intensification rate. The guidance is remarkably well clustered, with all of the hurricane models showing category 4 strength within 48 hours, which is uncommon given the current intensity. The new forecast continues to show rapid intensification and is increased 5 or 10 kt at most time periods, but it is still not as high as the Florida State Superensemble or the NOAA corrected consensus models. It is worth noting that the model guidance is also significantly increasing the size of Florence's wind field over the next few days, and the official forecast reflects this trend. The fixes from the aircraft indicate that Florence hasn't gained much latitude yet, and continues moving westward at about 6 kt. There is no change to the synoptic reason as a very strong ridge is forecast to build over the northwestern Atlantic during the next few days. This pattern should steer Florence west-northwestward at a much faster forward speed by Tuesday. On Wednesday, the hurricane will likely turn northwestward and slow down somewhat due to another ridge forming over the Ohio Valley. The most notable change from the previous advisory is that most of the models are showing a faster motion in 3 or 4 days, which unfortunately increases the risk of a destructive hurricane landfall. The GFS and its ensemble mean are outliers from the main model envelope, showing the system near the Outer Banks, while the rest of the guidance is well to the southwest. While a near-miss isn't impossible given the spread of the ECMWF Ensemble, there is much more support for a track to the southwest, especially considering the poleward bias of the GFS thus far this season. Therefore, the official track forecast is shifted a little bit to the southwest, and is very close to the corrected-consensus models. The NOAA G-IV jet is conducting a synoptic surveillance mission this afternoon to gather data near and around Florence for assimilation into the numerical models, and these missions will continue through Tuesday. In addition, upper-air stations across portions of the central and eastern U.S. are conducting special 0600 UTC and 1800 UTC radiosonde launches to collect extra data for the numerical models. Hopefully these data will help improve the track and intensity forecasts. Key Messages: 1. There is an increasing risk of two life-threatening impacts from Florence: storm surge at the coast and freshwater flooding from a prolonged heavy rainfall event inland. While it is too soon to determine the exact timing, location, and magnitude of these impacts, interests at the coast and inland from South Carolina into the mid-Atlantic region should closely monitor the progress of Florence, ensure they have their hurricane plan in place, and follow any advice given by local officials. 2. Large swells affecting Bermuda and portions of the U.S. East Coast will continue this week. These swells will result in life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 09/2100Z 24.4N 57.0W 75 KT 85 MPH 12H 10/0600Z 24.6N 58.3W 90 KT 105 MPH 24H 10/1800Z 25.1N 60.4W 105 KT 120 MPH 36H 11/0600Z 25.9N 63.1W 115 KT 130 MPH 48H 11/1800Z 27.0N 66.2W 125 KT 145 MPH 72H 12/1800Z 30.3N 72.6W 130 KT 150 MPH 96H 13/1800Z 33.5N 77.5W 120 KT 140 MPH 120H 14/1800Z 35.0N 79.0W 60 KT 70 MPH...INLAND $$ Forecaster Blake
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Hurricane Helene Forecast Discussion Number 10
2018-09-09 22:32:48| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Sep 09 2018 354 WTNT43 KNHC 092032 TCDAT3 Hurricane Helene Discussion Number 10 NWS National Hurricane Center Miami FL AL082018 500 PM AST Sun Sep 09 2018 Deep convection has increased in coverage and intensity over the southern portion of the circulation, and microwave imagery suggests that an inner core is beginning to develop. Helene's maximum winds are boosted to hurricane strength, 65 kt, based on Dvorak Current Intensity numbers from SAB and TAFB. The cyclone should continue to traverse warm waters and be in a low-shear environment for the next couple of days. Therefore, additional intensification is called for during the next 48 hours. Afterwards, increasing south-southwesterly shear should cause gradual weakening. The official intensity forecast is close to the model consensus, IVCN. Helene is moving just north of due west, or 280/11 kt. There are no significant changes to the track forecast philosophy for this advisory. Helene should move generally west-northwestward along the south side of a weak mid-level ridge for the next couple of days. After that, a mid-level trough digging along 40W-45W longitude should induce a turn toward the northwest and eventually north. The official track forecast is very similar to the one from the previous cycle through 72 hours, and is nudged a little to the east after that time. This is fairly close to the latest corrected consensus guidance, HCCA. FORECAST POSITIONS AND MAX WINDS INIT 09/2100Z 13.4N 26.0W 65 KT 75 MPH 12H 10/0600Z 13.9N 28.1W 75 KT 85 MPH 24H 10/1800Z 14.5N 30.8W 85 KT 100 MPH 36H 11/0600Z 15.2N 33.3W 90 KT 105 MPH 48H 11/1800Z 15.9N 35.5W 90 KT 105 MPH 72H 12/1800Z 18.0N 38.6W 80 KT 90 MPH 96H 13/1800Z 21.5N 40.5W 65 KT 75 MPH 120H 14/1800Z 27.5N 41.5W 55 KT 65 MPH $$ Forecaster Pasch
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