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Hurricane Maria Forecast Discussion Number 29

2017-09-23 10:53:24| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Sat Sep 23 2017 000 WTNT45 KNHC 230853 TCDAT5 Hurricane Maria Discussion Number 29 NWS National Hurricane Center Miami FL AL152017 500 AM EDT Sat Sep 23 2017 Maria is sending mixed signals regarding its intensity this morning. One one side, the 35 n mi wide eye has become better defined in satellite imagery, and the last report from an Air Force Reserve Hurricane Hunter aircraft indicated that the central pressure had fallen to 952 mb. On the other side, the aircraft-reported winds decreased a little since the previous advisory, with maximum 700-mb flight-level winds of 110 kt and maximum surface wind estimates from the Stepped Frequency Microwave Radiometer near 100 kt. Based on the aircraft winds, the initial intensity is lowered to 105 kt. Various analyses show that Maria is experiencing about 15 kt of southwesterly shear, which is likely the reason for an asymmetric distribution of convection in the eyewall at this time. The hurricane is likely to stay over warm water in an environment of light to moderate shear for the next 36-48 h. The intensity forecast during this time will show some fluctuations in strength, with the forecast lying near the upper edge of the intensity guidance. After 48 h, the forecast track takes Maria over the cold sea surface temperatures left behind by former hurricane Jose, which are below 26C in some areas. This should cause a pronounced weakening, and the new forecast is similar to the old forecast in showing such a trend during this time. The initial motion remains 345/8. Maria is currently being steered by a subtropical ridge to the east of the hurricane and a mid- to upper-level trough over the southeastern United States. This combination should cause a north-northwestward to northward motion for the next couple of days. After that, the ridge is forecast to amplify toward the northwest due to the influence of a mid- to upper-level ridge in the westerlies moving through the northeastern United States. The track guidance has responded to this evolution by shifting westward since the last advisory, with several of the global models now calling for Maria to come close enough to the U. S. east coast to cause direct impacts before the system recurves into the westerlies around 120 h. The latter part of the forecast track is also shifted to the west, but it lies to the east of the consensus models and the center of the guidance envelope. If the current model trends continue, additional westward adjustments to the track forecast will be necessary later today. KEY MESSAGES: 1. Swells from Maria are expected to increase along the coast of the southeastern United States and will likely cause dangerous surf and life-threatening rip currents for the next several days. 3. Maria will likely move between the east coast of the United States and Bermuda by the middle of next week. While the forecast track has moved closer to the U. S. east coast, it is still too soon to determine what, if any, direct impacts there might be in these areas. 4. For more information on the flooding and rip current hazards in the United States, please monitor information from your local National Weather Service forecast office at www.weather.gov. FORECAST POSITIONS AND MAX WINDS INIT 23/0900Z 24.8N 72.0W 105 KT 120 MPH 12H 23/1800Z 26.0N 72.4W 110 KT 125 MPH 24H 24/0600Z 27.7N 72.7W 110 KT 125 MPH 36H 24/1800Z 29.2N 72.9W 105 KT 120 MPH 48H 25/0600Z 30.3N 73.0W 100 KT 115 MPH 72H 26/0600Z 32.0N 73.0W 85 KT 100 MPH 96H 27/0600Z 34.0N 73.0W 70 KT 80 MPH 120H 28/0600Z 36.0N 71.5W 65 KT 75 MPH $$ Forecaster Beven

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Tropical Storm Lee Forecast Discussion Number 19

2017-09-23 04:52:46| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Sep 22 2017 000 WTNT44 KNHC 230252 TCDAT4 Tropical Storm Lee Discussion Number 19 NWS National Hurricane Center Miami FL AL142017 1100 PM AST Fri Sep 22 2017 Several microwave overpasses between 2100 and 2200 UTC indicated that Lee was becoming better organized, at least at the mid-levels. In particular, a WindSat overpass near 21Z indicated that a mid-level eye was already forming. Since that time, however, cloud tops have warmed, the CDO has shrunk, and a GPM overpass around 0100 UTC showed that most of the convection is currently confined to the southeast semicircle of the tropical storm. The UW-CIMSS ADT supports an intensity of 35 kt, and the TAFB Dvorak analyst indicated that the subjective classification would have been higher, if the technique wasn't constrained by the fact that classifications on Lee only recently restarted. Based on these data, the initial intensity has been increased to 35 kt. The intensity forecast for Lee is highly uncertain. The tropical storm is very small, and small cyclones often quickly strengthen or weaken. Furthermore, Lee is small enough that some of our models (and many of our observing platforms) may have trouble resolving the inner core of the storm. Given the current convective state of Lee, significant strengthening in the short term seems unlikely. However, the cyclone is expected to be in a fairly unstable, low shear environment for at least the next 3 days, so it is possible that rapid intensification could occur at some time during that period. On the other hand, I can't rule out that the cyclone could dissipate entirely, as depicted by the GFS, within a couple days. For now, my forecast is closest to the HWRF for the first 72 h, since that model tends to do well in low-shear environments and should have sufficient resolution to model Lee's core. After that time, the forecast is close to the HCCA and IVCN intensity consensus models. Lee has continued to move north around 6 kt. Little change has been made to the track forecast, and Lee is still forecast to move around a subtropical ridge for the next 72 h. At days 4 and 5, a ridge building between Lee and Maria to the west should cause a turn more toward the south, as long as Lee is sufficiently deep to be steered by that feature. The forecast continues to be close to the ECMWF, since it is still the global model with the strongest representation of Lee, in line with the NHC forecast. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 31.5N 49.0W 35 KT 40 MPH 12H 23/1200Z 32.2N 48.5W 40 KT 45 MPH 24H 24/0000Z 32.5N 47.8W 45 KT 50 MPH 36H 24/1200Z 32.4N 46.6W 50 KT 60 MPH 48H 25/0000Z 32.1N 45.2W 60 KT 70 MPH 72H 26/0000Z 31.3N 43.1W 75 KT 85 MPH 96H 27/0000Z 30.0N 42.5W 75 KT 85 MPH 120H 28/0000Z 29.5N 43.5W 65 KT 75 MPH $$ Forecaster Zelinsky

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Hurricane Maria Forecast Discussion Number 28

2017-09-23 04:36:56| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Fri Sep 22 2017 000 WTNT45 KNHC 230236 TCDAT5 Hurricane Maria Discussion Number 28 NWS National Hurricane Center Miami FL AL152017 1100 PM EDT Fri Sep 22 2017 A NOAA Hurricane Hunter plane and the Coyote unmanned aerial vehicle launched from the NOAA plane have sampled the eye and the surroundings of Maria early this evening. An Air Force plane also arrived and so far has penetrated the eye a couple of times. Based on the data from these platforms, the maximum winds are still 110 kt in the eyewall that surrounds a large eye of about 35 n mi in diameter. There are no reports of a double wind max at this time so no eyewall replacement cycle is anticipated soon. The current shear is forecast to decrease, but the hurricane is moving toward a region with less oceanic heat content. The combination of these two factors should result in a very gradual decay of the hurricane, and the NHC forecast keeps Maria as a category 3 at least for one or two more days. Satellite and plane fixes indicate that Maria is moving toward the north-northwest or 345 degrees at 8 kt, steered by a subtropical ridge to the east of the hurricane. The ridge is forecast to amplify westward during the next few days, but it is not expected to be strong enough to block the northward motion of the hurricane. It will however, force the hurricane to move slowly. Tonight's guidance continues to be in very good agreement for the next 3 days, and the NHC forecast is in the middle of the tight envelope. After that time, the GFS and EMWF are once again in competition, with the GFS defining the western edge of the guidance envelope and the ECMWF the eastern one. This makes the forecast a little more uncertain. The NHC forecast recurves Maria over the open Atlantic which is the solution of the HFIP corrected consensus and the multi-model consensus. KEY MESSAGES: 1. Swells from Maria are expected to increase along the coast of the southeastern United States and will likely cause dangerous surf and life-threatening rip currents for the next several days. 3. Maria will move between the east coast of the United States and Bermuda by the middle of next week, but it is too soon to determine what, if any, direct impacts there might be in these areas. 4. For more information on the flooding and rip current hazards in the United States, please monitor information from your local National Weather Service forecast office at www.weather.gov. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 24.1N 71.7W 110 KT 125 MPH 12H 23/1200Z 25.3N 72.1W 110 KT 125 MPH 24H 24/0000Z 27.0N 72.4W 105 KT 120 MPH 36H 24/1200Z 28.5N 72.7W 100 KT 115 MPH 48H 25/0000Z 29.7N 72.8W 95 KT 110 MPH 72H 26/0000Z 31.7N 72.4W 85 KT 100 MPH 96H 27/0000Z 33.5N 72.3W 75 KT 85 MPH 120H 28/0000Z 35.5N 71.0W 65 KT 75 MPH $$ Forecaster Avila

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Staff responses to Discussion Draft public comments

2017-09-23 03:27:44| PortlandOnline

PDF Document, 846kbCategory: TSP Update - Stage 3 (In Progress)

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Hurricane Maria Forecast Discussion Number 27

2017-09-22 22:41:10| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Fri Sep 22 2017 000 WTNT45 KNHC 222041 TCDAT5 Hurricane Maria Discussion Number 27 NWS National Hurricane Center Miami FL AL152017 500 PM EDT Fri Sep 22 2017 A ragged eye has re-appeared during the past several hours, but overall the satellite presentation of Maria has not changed much during the past several hours. The initial intensity is therefore held at 110 kt pending data new data from an ongoing NOAA research mission and an upcoming Air Force Reserve flight. According to various analyses, Maria is under the influence of 20 kt of shear from the southwest, which has apparently eroded the eyewall a bit on that side of the storm. This shear may abate some in about 24 hours, although Maria will also be moving over an area of gradually lowering oceanic heat content. Maria's intensity is therefore only expected to decrease very gradually during the next 48 hours. After that time, the shear is expected to pick up again, and Maria will be moving over the cold wake left behind by Jose. As a result, a steadier weakening should ensue on days 3 through 5. The NHC intensity forecast remains closest to the ICON intensity consensus and is relatively unchanged from the previous advisory. Maria is turning around the southwestern periphery of a mid-level high centered south of Bermuda, and the initial motion estimate is 335/8 kt. The hurricane should turn northward by 36 hours when it moves between the high and a developing cut-off low near the U.S. Gulf coast, and that northward motion, with some east-west wiggles, is likely to continue through day 5. The new track models have shifted significantly westward on this cycle, leaving the interpolated version of the previous forecast (OFCI) by itself on the eastern edge of the guidance suite. Oddly enough, the ECMWF model went from being on the west side of the guidance envelope to the east side, so the westward shift of the new NHC forecast on days 3 through 5 only goes as far as that model and the TVCN consensus. KEY MESSAGES: 1. Flooding continues in portions of Puerto Rico and the Dominican Republic due to Maria's heavy rains over the past few days. Continue to follow advice from local officials to avoid these life-threatening flooding conditions. 2. Swells from Maria are affecting the coast of the southeastern United States and will likely cause dangerous surf and life- threatening rip currents for the next several days. 3. Maria will move between the east coast of the United States and Bermuda by the middle of next week, but it is too soon to determine what, if any, direct impacts there might be in these areas. 4. For more information on the flooding and rip current hazards in the United States, please monitor information from your local National Weather Service forecast office at www.weather.gov. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 23.3N 71.4W 110 KT 125 MPH 12H 23/0600Z 24.3N 71.8W 105 KT 120 MPH 24H 23/1800Z 25.9N 72.2W 105 KT 120 MPH 36H 24/0600Z 27.5N 72.5W 100 KT 115 MPH 48H 24/1800Z 28.8N 72.5W 95 KT 110 MPH 72H 25/1800Z 30.7N 72.0W 85 KT 100 MPH 96H 26/1800Z 32.5N 72.0W 75 KT 85 MPH 120H 27/1800Z 34.5N 71.5W 65 KT 75 MPH $$ Forecaster Berg

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