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Tropical Storm NICOLE Forecast Discussion Number 16

2016-10-08 04:52:02| National Hurricane Center (Atlantic)

Issued at 1100 PM AST FRI OCT 07 2016 000 WTNT45 KNHC 080251 TCDAT5 TROPICAL STORM NICOLE DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL152016 1100 PM AST FRI OCT 07 2016 Strong northerly shear continues to cause all of Nicole's deep convection to be located in the southern semicircle of the storm. The deep convection has been going up and down, very typical for this type of sheared tropical cyclone. ASCAT showed a sizable area of winds near 45 kt, and after considering the low bias of the instrument for a small tropical cyclone, the initial wind speed is reduced to 50 kt. This is also consistent with a blend of the Dvorak T- and CI-numbers from TAFB. Nicole is moving southward at about 6 kt. A motion toward the south or south-southeast is anticipated for the next day or so while the tropical cyclone is steered on the east side of a mid-level high between Nicole and Matthew. The forecast gets very tricky in a couple of days, with the mid-level high breaking down and Matthew probably moving toward Nicole. The possibility of tropical cyclone binary interaction appears to be increasing, which could cause Nicole to move toward the north or north-northwest in the 3 to 5 day period. The details of this interaction, however, are very sketchy, with models presenting a variety of fairly divergent solutions. The new NHC forecast is close to the ensemble means of the UKMET, ECMWF and GFS, which ends up south of the previous forecast at short range, and to the east of the previous forecast at long range. These are relatively small changes since it is probably best not to move the forecast very much until the models come into better agreement on the final phase of Matthew. Northerly shear is forecast to continue near Nicole over the next two or three days. Models do not show as much weakening as one might think, perhaps due to the very warm water that Nicole will be traversing, or due to Nicole's possible interaction with a shortwave trough. After that time, global models generally show a decrease in shear and a diffluent upper-level pattern, which would support some restrengthening. The model guidance is slightly higher than the last cycle, and the latest NHC prediction is nudged in that direction, although the new forecast is on the low side of the guidance. Needless to say, this is a fairly uncertain forecast overall because Matthew could play a large role in a few days. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 26.3N 65.3W 50 KT 60 MPH 12H 08/1200Z 25.5N 65.1W 45 KT 50 MPH 24H 09/0000Z 24.7N 64.9W 45 KT 50 MPH 36H 09/1200Z 24.8N 65.2W 45 KT 50 MPH 48H 10/0000Z 25.5N 65.5W 45 KT 50 MPH 72H 11/0000Z 27.7N 65.8W 45 KT 50 MPH 96H 12/0000Z 30.5N 66.0W 50 KT 60 MPH 120H 13/0000Z 33.5N 65.5W 60 KT 70 MPH $$ Forecaster Blake

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Hurricane MATTHEW Forecast Discussion Number 39

2016-10-07 22:47:01| National Hurricane Center (Atlantic)

Issued at 500 PM EDT FRI OCT 07 2016 000 WTNT44 KNHC 072046 TCDAT4 HURRICANE MATTHEW DISCUSSION NUMBER 39 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142016 500 PM EDT FRI OCT 07 2016 Data from a NOAA Hurricane Hunter plane and satellite intensity estimates indicate that Matthew has weakened a little bit and the maximum winds are 95 kt. The hurricane is heading toward an area of increasing shear, and this should result in gradual weakening. The shear is forecast to continue during the next 5 days, so additional weakening is anticipated and Matthew is expected to be a tropical depression by the end of the forecast period. Matthew has begun to move northward at about 10 kt. In about 12 hours, the hurricane will encounter the mid-latitude westerlies, and this flow pattern should induce a northeastward and then eastward motion during the next 2 days. During that time the core of the hurricane is expected to hug the coast from Georgia through southeastern North Carolina. The confidence in this portion of the track forecast is high. After that time, the steering flow becomes very complex, and both the GFS and ECMWF models turn the cyclone southward and southwestward embedded within the flow on the west side of a mid-level trough. The NHC track follows these two models, but the confidence is portion of the forecast is low. KEY MESSAGES: 1. We have been very fortunate that Matthew's strongest winds have remained a short distance offshore of the Florida Coast thus far, but this should not be a reason to let down our guard. Only a small deviation to the left of the forecast track could bring these winds onshore. The western eyewall of Matthew, which contains hurricane-force winds, is expected to move over or very near the coast of northeastern Florida and Georgia through tonight. 2. Hurricane winds increase very rapidly with height, and occupants of high-rise buildings in the Jacksonville area are at particular risk of strong winds. Winds at the top of a 30-story building will average one Saffir-Simpson category higher than the winds near the surface. 3. The water hazards remain, even if the core of Matthew remains offshore. These include the danger of life-threatening inundation from storm surge, as well as inland flooding from heavy rains from Florida to North Carolina. 4. The National Hurricane Center is issuing Potential Storm Surge Flooding Maps, and Prototype Storm Surge Watch/Warning Graphics for Matthew. It is important to remember that the Potential Storm Surge Flooding Map does not represent a forecast of expected inundation, but rather depicts a reasonable worst-case scenario -- the amount of inundation that has a 10 percent chance of being exceeded. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 30.2N 80.7W 95 KT 110 MPH 12H 08/0600Z 31.7N 80.7W 90 KT 105 MPH 24H 08/1800Z 33.0N 79.0W 80 KT 90 MPH 36H 09/0600Z 33.8N 76.7W 65 KT 75 MPH 48H 09/1800Z 33.5N 75.0W 60 KT 70 MPH 72H 10/1800Z 30.0N 74.5W 40 KT 45 MPH 96H 11/1800Z 27.0N 76.0W 35 KT 40 MPH 120H 12/1800Z 26.0N 77.0W 30 KT 35 MPH $$ Forecaster Avila

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Tropical Storm NICOLE Forecast Discussion Number 15

2016-10-07 22:36:55| National Hurricane Center (Atlantic)

Issued at 500 PM AST FRI OCT 07 2016 000 WTNT45 KNHC 072036 TCDAT5 TROPICAL STORM NICOLE DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL152016 500 PM AST FRI OCT 07 2016 Nicole is a heavily sheared tropical cyclone. The well-defined low-level center is partially exposed on the northwest side of a bursting mass of deep convection. Dvorak Final-T numbers have continued to decrease to T3.0 from both satellite agencies, and a blend of those with CI-numbers yields an initial intensity of 55 kt. Nicole has begun to move southward, and the initial motion estimate is 185/04. A blocking high north of Nicole should continue to push the cyclone slowly southward during the next couple of days. After that time, the mid-level ridge is forecast to rebuild east of Nicole, and there is the potential for a binary interaction with weakening Matthew to the west in 2 to 3 days. This should cause Nicole to do an about-face and begin moving northwestward or north-northwestward from days 2 to 4. A turn toward the north is expected by day 5 once the binary interaction ends and Nicole is on the cusp of entering a stronger mid-latitude southwesterly flow. Although the bulk of the model guidance is in basic agreement with this scenario, there are speed differences amongst the models that make the track forecast of lower confidence than average. Global models show no diminution of the northerly shear over Nicole for the next two days or so. A further complication is Nicole's interaction during this same time period with a fractured lobe of vorticity from a shortwave trough to the east that wraps around the circulation. The net result of all of this is that the cyclone could weaken a bit further or remain steady state as a weak tropical storm for 2 to 3 days, which is what the official forecast and SHIPS model output indicates. After that time, the shear is forecast to decrease and the flow aloft is likely to become much more diffluent, both of which support some re-intensification. This is shown in the latter part of the forecast period, which likewise is in good agreement with SHIPS model output. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 27.0N 65.2W 55 KT 65 MPH 12H 08/0600Z 26.2N 65.0W 45 KT 50 MPH 24H 08/1800Z 25.4N 64.8W 40 KT 45 MPH 36H 09/0600Z 25.1N 64.9W 40 KT 45 MPH 48H 09/1800Z 25.5N 65.3W 40 KT 45 MPH 72H 10/1800Z 27.4N 66.0W 45 KT 50 MPH 96H 11/1800Z 29.7N 66.7W 50 KT 60 MPH 120H 12/1800Z 32.6N 66.4W 60 KT 70 MPH $$ Forecaster Kimberlain

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Hurricane MATTHEW Forecast Discussion Number 38

2016-10-07 16:59:30| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT FRI OCT 07 2016 000 WTNT44 KNHC 071459 TCDAT4 HURRICANE MATTHEW DISCUSSION NUMBER 38 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142016 1100 AM EDT FRI OCT 07 2016 The satellite presentation has degraded during the past several hours, and the eye is not very distinct. However, the SFMR and flight-level wind data from an Air Force reconnaissance plane indicate that the initial intensity is still 105 kt. Matthew is expected to change little in intensity during the next 6 to 12 hours, but it should begin to weaken at a faster pace in 24 hours while the shear increases, and by the end of the forecast period, Matthew is expected to become a tropical depression. Fixes from a reconnaissance plane indicate that Matthew is moving toward the north-northwest or 345 degrees at 10 kt. Matthew is reaching the northwestern edge of the subtropical ridge and encounter the mid-latitude westerlies. This flow pattern should steer the hurricane northward and then northeastward during the next 36 hours. After that time, the flow pattern is forecast to change again and a weakening Matthew should then turn southward and southwestward. The NHC forecast is a little bit to the north from the previous one during the first 24 to 36 hour period following the multi-model consensus. After 72 hours, models continue to vary the flow pattern and the confidence in the track forecast is low. KEY MESSAGES: 1. We have been very fortunate that Matthew's category 3 winds have remained a short distance offshore of the Florida Coast thus far, but this should not be a reason to let down our guard. Only a small deviation to the left of the forecast track could bring these winds onshore. The western eyewall of Matthew, which contains hurricane-force winds, is expected to move over or very near the coast of northeastern Florida and Georgia today. 2. Hurricane winds increase very rapidly with height, and occupants of high-rise buildings in the Jacksonville area are at particular risk of strong winds. Winds at the top of a 30-story building will average one Saffir-Simpson category higher than the winds near the surface. 3. The water hazards remain, even if the core of Matthew remains offshore. These include the danger of life-threatening inundation from storm surge, as well as inland flooding from heavy rains from Florida to North Carolina. 4. The National Hurricane Center is issuing Potential Storm Surge Flooding Maps, and Prototype Storm Surge Watch/Warning Graphics for Matthew. It is important to remember that the Potential Storm Surge Flooding Map does not represent a forecast of expected inundation, but rather depicts a reasonable worst-case scenario -- the amount of inundation that has a 10 percent chance of being exceeded. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 29.4N 80.4W 105 KT 120 MPH 12H 08/0000Z 30.8N 80.7W 100 KT 115 MPH 24H 08/1200Z 32.5N 79.9W 85 KT 100 MPH 36H 09/0000Z 33.5N 78.1W 75 KT 85 MPH 48H 09/1200Z 33.5N 76.0W 60 KT 70 MPH 72H 10/1200Z 32.0N 74.0W 50 KT 60 MPH 96H 11/1200Z 28.0N 75.0W 35 KT 40 MPH 120H 12/1200Z 27.0N 76.0W 30 KT 35 MPH $$ Forecaster Avila

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Tropical Storm NICOLE Forecast Discussion Number 14

2016-10-07 16:36:34| National Hurricane Center (Atlantic)

Issued at 1100 AM AST FRI OCT 07 2016 000 WTNT45 KNHC 071436 TCDAT5 TROPICAL STORM NICOLE DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL AL152016 1100 AM AST FRI OCT 07 2016 Strong shear has taken its toll on Nicole overnight. The cyclone's cloud pattern has rapidly deteriorated, with the low-level center now exposed to the northwest of a greatly reduced area of deep convection. Dvorak Final T-numbers have decreased quickly to T3.5 from SAB and TAFB, and a blend of these and CI-numbers was used to set the initial intensity to 65 kt at 1200 UTC. Since the cloud pattern has degraded even further since that time, the advisory intensity is lowered to 60 kt, which could prove to be generous. Nicole has barely been moving, and the initial motion estimate is nearly stationary. Although Nicole remains in a region of weak steering at the moment, a blocking mid-level high should build north of the cyclone soon, and impart a slow motion generally toward the south for the next couple of days. Around 48 hours, a mid-level ridge is forecast to develop to the east of Nicole, which should result in the cyclone gradually turning northward with some increase in forward speed through the remainder of the forecast period. Most of the model guidance is in better agreement than yesterday on this scenario, which increases the overall confidence of the track forecast. The new track forecast is based on a consensus of the regional and global models minus the GFDL. A potent mid- to upper-level shortwave trough digging to the east of Nicole should cause deep-layer northerly shear over the cyclone to increase further today. In the wake of the shortwave, the shear should veer to the north-northeast but remain just as strong through about 72 hours. Nicole is also shown interacting with a lobe of vorticity that fractures from the shortwave, but it remains unclear how this interaction would affect the cyclone's intensity or structure. Regardless, the overall hostile environment should cause weakening, perhaps even more than indicated in this forecast. Indications are that late in the forecast period the large- scale environment should become more conducive for Nicole to re-intensify, but to what extent is in doubt. As a result of developments overnight, the new intensity forecast is substantially lower than the previous one and is below all of the intensity guidance through 72 hours. It is near the multi-model consensus after that time, although this part of the forecast is of low confidence. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 27.5N 65.3W 60 KT 70 MPH 12H 08/0000Z 27.0N 65.1W 50 KT 60 MPH 24H 08/1200Z 26.1N 64.8W 45 KT 50 MPH 36H 09/0000Z 25.4N 64.7W 40 KT 45 MPH 48H 09/1200Z 25.3N 65.1W 40 KT 45 MPH 72H 10/1200Z 26.6N 65.7W 35 KT 40 MPH 96H 11/1200Z 28.8N 66.1W 40 KT 45 MPH 120H 12/1200Z 32.0N 65.6W 50 KT 60 MPH $$ Forecaster Kimberlain

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