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Tropical Storm Nicholas Forecast Discussion Number 2

2021-09-12 23:01:41| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Sun Sep 12 2021 000 WTNT44 KNHC 122101 TCDAT4 Tropical Storm Nicholas Discussion Number 2 NWS National Hurricane Center Miami FL AL142021 400 PM CDT Sun Sep 12 2021 Visible satellite imagery, scatterometer wind data, and earlier reconnaissance aircraft observations indicate that the circulation of Nicholas is elongated from northwest to southeast. In fact, visible satellite imagery and the aircraft data has shown that there have been several low-level swirls rotating about a mean center. This is not surprising since the tropical cyclone is still in its formative stage. The Air Force plane did not find winds any stronger than they did this morning and the ASCAT data revealed peaks winds of around 30 kt. Given the typical undersampling of the scatterometer instrument, the earlier aircraft data, and peak one-minute wind observations of 31 kt from NOAA buoy 42055 earlier today, the intensity remains 35 kt for this advisory. Nicholas will be moving over the warm waters of the western Gulf of Mexico during the next day or so, and this combined with a moist, unstable atmosphere favors strengthening. The primarily inhibiting factor appears to be moderate south-southwesterly vertical wind shear caused by an upper-level trough over northern Mexico. The trough is forecast to move westward and weaken during the next day or so, which could allow for a more favorable upper-level wind pattern later tonight and Monday. The NHC intensity forecast again calls for strengthening while the system moves toward the northwest Gulf coast, but the main uncertainty regarding the intensity forecast is how much time the cyclone will spend over the Gulf waters. The GFS and HWRF models, which depict a track farther east, show significantly more strengthening than the UKMET and ECMWF models which show a weaker tropical cyclone moving inland over northeastern Mexico or southern Texas much sooner. The NHC intensity forecast is similar to the previous advisory, but indicates a faster rate of strengthening during the next 12-24 hours. Although not explicitly shown in the intensity forecast, Nicholas could approach hurricane strength when it nears the northwest Gulf coast, especially if it moves to the right of the NHC forecast track and spends more time over water. Due to this uncertainty a Hurricane Watch has been issued a for a portion of the Texas coast. The NHC forecast is in best agreement with the SHIPS and HFIP corrected consensus model, but is not as high as the latest HWRF. The center of Nicholas appears to have re-formed farther north since this morning and the initial motion estimate is again a somewhat uncertain 340/12 kt. The track forecast reasoning has not changed from this morning. Nicholas should move north-northwestward to northward during the next day or so around the western portion of a mid-level ridge that is located near the southeast U.S. coast. The latest runs of the various dynamical models have shown typical variability, but the overall guidance envelope has not changed too much through the first 36 hours. The GFS has been the most consistent model and its 12Z run was fairly close to the previous NHC track forecast. Therefore, the NHC track leans along the right side of the guidance envelope between the HWRF and GFS, which are a little to the right of the consensus aids. Due to the acute angle of approach of Nicholas to the coast, users are reminded to not focus on the exact forecast track as small changes in the heading of the cyclone could result in differences in both the location and timing of landfall. Regardless of where Nicholas makes landfall, storm surge, wind, and rainfall impacts are likely over a large portion of northeastern Mexico and Texas coastal areas. After landfall, a slower north-northeastward motion is forecast, and by 72 hours the cyclone is forecast to be located between a couple of mid-level ridges, which will likely result in weaker steering currents and an even slower northeastward motion. By day 5, the global model guidance suggest that the low-level circulation will become an open trough so dissipation is indicated at that time. Key Messages: 1. Periods of heavy rainfall are expected to impact portions of the Texas and Louisiana coasts today through the middle of the week. Significant rainfall amounts are possible, potentially resulting in areas of considerable flash and urban flooding, especially in highly urbanized metropolitan areas. Isolated minor to moderate river flooding is also expected. 2. There is the danger of life-threatening storm surge inundation along the coast of Texas from Port Aransas to San Luis Pass. Residents in these areas should follow any advice given by local officials. 3. Nicholas is forecast to approach the middle Texas coast as a strong tropical storm late Monday and early Tuesday, and could be near hurricane intensity if it moves to the right of the forecast track and remains over water longer. Tropical storm conditions are expected along portions of the middle Texas coast beginning Monday afternoon, with hurricane conditions possible from Port Aransas to Sargent late Monday and Monday night. 4. Tropical storm conditions are expected along portions of the northeastern coast of Mexico and the coast of south Texas beginning Monday morning. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 22.8N 95.5W 35 KT 40 MPH 12H 13/0600Z 24.4N 96.3W 45 KT 50 MPH 24H 13/1800Z 26.7N 96.9W 55 KT 65 MPH 36H 14/0600Z 28.7N 96.8W 55 KT 65 MPH...INLAND 48H 14/1800Z 30.4N 96.3W 35 KT 40 MPH...INLAND 60H 15/0600Z 31.2N 95.8W 30 KT 35 MPH...INLAND 72H 15/1800Z 31.7N 95.2W 25 KT 30 MPH...INLAND 96H 16/1800Z 31.9N 94.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 17/1800Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Nicholas Forecast Discussion Number 1

2021-09-12 17:03:02| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Sun Sep 12 2021 000 WTNT44 KNHC 121502 TCDAT4 Tropical Storm Nicholas Discussion Number 1 NWS National Hurricane Center Miami FL AL142021 1000 AM CDT Sun Sep 12 2021 Showers and thunderstorms associated with a broad area of low pressure over the southern Bay of Campeche have increased overnight and very recently become better organized with a loose band of convection around the northeastern portion of the circulation. An Air Force Reserve reconnaissance aircraft that has been investigating the system has found 44-kt flight-level winds and SFMR winds that support a 35-kt initial intensity. Based on the recent increase in organization and the 35-kt initial intensity, advisories are being initiated on Tropical Storm Nicholas, the fourteenth named storm of the Atlantic hurricane season. The storm is located within an environment of moderate south-southwesterly vertical wind shear, over warm waters, and in a moist and unstable atmosphere. These conditions should allow gradual strengthening over the next 24 to 48 hours. The NHC intensity forecast follows suit and calls for gradual strengthening until the system reaches the coast of Texas. The official wind speed forecast is near the higher end of the guidance in best agreement with the SHIPS statistical guidance, the HFIP corrected consensus, and the HWRF. In this case, the intensity forecast is highly dependent on eventual track of the system. A track to the east of the NHC forecast could result in a lower wind shear environment and slightly more time over water for the system to strengthen. Conversely a track to the west of the forecast track would result in the system interacting with land much sooner. Since the system is still in its formative stage the initial motion estimate is a somewhat uncertain 330/11 kt. A north-northwestward motion around the western portion of a mid-level ridge that is sliding east near the coast of the Carolinas, should continue to steer Nicholas in that direction for the next 24 to 48 hours. After that time, steering currents weaken and the cyclone is expected to move slowly north-northeastward between a couple of mid-level ridges located to the east and west of Nicholas. The track guidance generally agrees with this overall scenario but there is some cross-track spread with the UKMET along the left side of the guidance envelope taking the storm into northeastern Mexico, while the GFS, HWRF, and HMON are along the right side. The NHC track is near the various consensus models and both the EC and GFS ensemble means. Key Messages: 1. Tropical storm conditions are expected along portions of the northeastern coast of Mexico and the coast of south Texas beginning on Monday. Nicholas is forecast to approach the middle Texas coast as a strong tropical storm on Tuesday, and tropical storm conditions are possible along portions of the middle and upper Texas coasts late Monday night and Tuesday. 2. There is the possibility of life-threatening storm surge along the coast of Texas from the Mouth of the Rio Grande to High Island. Residents in these areas should follow any advice given by local officials. 3. Periods of heavy rainfall are expected to impact portions of the Texas and Louisiana coasts today through the middle of the week. Significant rainfall amounts are possible, potentially resulting in areas of flash, urban, and isolated river flooding. FORECAST POSITIONS AND MAX WINDS INIT 12/1500Z 20.5N 94.8W 35 KT 40 MPH 12H 13/0000Z 21.9N 95.7W 40 KT 45 MPH 24H 13/1200Z 24.1N 96.6W 45 KT 50 MPH 36H 14/0000Z 26.4N 96.9W 50 KT 60 MPH 48H 14/1200Z 28.2N 96.5W 55 KT 65 MPH 60H 15/0000Z 29.4N 95.9W 40 KT 45 MPH...INLAND 72H 15/1200Z 30.3N 95.2W 30 KT 35 MPH...INLAND 96H 16/1200Z 31.0N 94.8W 25 KT 30 MPH...INLAND 120H 17/1200Z 32.0N 94.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Post-Tropical Cyclone Larry Forecast Discussion Number 44

2021-09-11 16:38:06| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 11 2021 000 WTNT42 KNHC 111437 TCDAT2 Post-Tropical Cyclone Larry Discussion Number 44 NWS National Hurricane Center Miami FL AL122021 1100 AM AST Sat Sep 11 2021 Satellite images indicate that Larry has completed its transition to a post-tropical cyclone with most of the deep convection dissipating near the low-level center and frontal features developing. In addition, the low- and mid-level centers are now well separated, and the cyclone appears a little weaker. The initial intensity is estimated to be 60 kt. The post-tropical system is very large and gale-force winds and high seas extend far from the center. It is interesting to note that up to just several hours ago Larry had maintained an inner core and a fairly tropical appearance despite being at very high latitudes and over quite cold water. Larry is racing northeastward, with the initial motion estimated to be 030/42 kt. The storm is expected to merge with another large extratropical low tonight or early Sunday. This is the last NHC advisory on Larry. For more information on this system, see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFAT1, WMO header FZNT01 KWBC, and online at ocean.weather.gov/shtml/NFDHSFAT1.php Key Messages: 1. Large swells generated by Post-Tropical Cyclone Larry will continue to affect portions of the the east coast of the United States and Atlantic Canada through tonight. These swells will cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 54.0N 48.2W 60 KT 70 MPH...POST-TROPICAL 12H 12/0000Z 57.8N 44.9W 55 KT 65 MPH...POST-TROP/EXTRATROP 24H 12/1200Z...DISSIPATED $$ Forecaster Cangialosi

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Post-Tropical Cyclone Olaf Forecast Discussion Number 15

2021-09-11 10:34:26| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Sat Sep 11 2021 000 WTPZ45 KNHC 110834 TCDEP5 Post-Tropical Cyclone Olaf Discussion Number 15 NWS National Hurricane Center Miami FL EP152021 300 AM MDT Sat Sep 11 2021 Olaf has been without deep convection for about the last 18 hours, and it is therefore being designated as a remnant low. A scatterometer pass from several hours ago still showed winds of 25-30 kt occurring to the north of the center, so the initial intensity remains 30 kt. Weakening is expected during the next few days while the remnant low traverses waters of about 25 degrees Celsius and through a very dry air mass. Global model fields show the circulation opening up into a trough anywhere between 2 and 6 days from now, so as a compromise the official forecast indicates this happening by day 4, but it's likely to be sooner than that. Olaf is now losing latitude and moving south of due west, or 260/5 kt. A strengthening low- to mid-level ridge to the north is expected to force the remnant low to the west-southwest and southwest during the next several days. In fact, the models have been trending toward a more pronounced loss of latitude, and this final NHC track forecast has been shifted southward from the previous advisory--close to the TVCE model consensus but not nearly as far south as the HCCA aid. For additional information on the remnant low please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at ocean.weather.gov/shtml/NFDHSFEPI.php FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 24.4N 114.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 12H 11/1800Z 24.2N 114.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 12/0600Z 23.7N 115.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 12/1800Z 22.8N 116.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 13/0600Z 21.5N 118.2W 15 KT 15 MPH...POST-TROP/REMNT LOW 60H 13/1800Z 20.6N 119.4W 15 KT 15 MPH...POST-TROP/REMNT LOW 72H 14/0600Z 20.1N 120.3W 15 KT 15 MPH...POST-TROP/REMNT LOW 96H 15/0600Z...DISSIPATED $$ Forecaster Berg

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Hurricane Larry Forecast Discussion Number 43

2021-09-11 10:32:24| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Sep 11 2021 000 WTNT42 KNHC 110832 TCDAT2 Hurricane Larry Discussion Number 43 NWS National Hurricane Center Miami FL AL122021 500 AM AST Sat Sep 11 2021 Larry made landfall near South East Bight, Newfoundland, around 0345 UTC. Since then, the hurricane has moved quickly north- northeastward at 42 kt and is now well northeast of Newfoundland. Although the hurricane still has some central convection, the low- and mid-level centers are separating, and the remaining convection is decreasing. The initial winds are lowered to 65 kt, consistent with the degraded structure. Larry should quickly transition into a strong post-tropical cyclone later today while it continues its speedy north-northeastward course, then dissipate as it merges with a developing mid-latitude low over the Labrador Sea. No significant changes were made to the track or intensity forecasts. Key Messages: 1. Large swells generated by Larry will continue to affect the Bahamas, Bermuda, the east coast of the United States, and Atlantic Canada through tonight. These swells will cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 50.7N 51.7W 65 KT 75 MPH 12H 11/1800Z 56.0N 46.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 24H 12/0600Z...DISSIPATED $$ Forecaster Blake

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