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Tropical Storm Maria Forecast Discussion Number 50
2017-09-28 16:50:53| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Sep 28 2017 000 WTNT45 KNHC 281450 TCDAT5 Tropical Storm Maria Discussion Number 50 NWS National Hurricane Center Miami FL AL152017 1100 AM AST Thu Sep 28 2017 A burst of strong convection containing cloud top temperatures colder than -70C has developed just east of the center since the previous advisory. Based on the recent inner-core convective development and a Dvorak current intensity estimate of 3.5/55 kt, the initial intensity estimate is being maintained at 60 kt for this advisory. Also, the last AMSU overpass around 0200 UTC indicated that Maria has retained tropical characteristics based on a deep warm core that extends from near the surface to above the 200 mb level, accompanied by a warm anomaly of more than 2.5 deg C, present in the upper-levels of the cyclone. Maria is now situated on the north side of a strong deep-layer ridge, and the initial motion estimate is now toward the east or 085/11 kt. The cyclone is expected to move in a general easterly direction for the next 12-24 h along the northern edge of the aforementioned ridge. Afterwards, Maria is forecast to get caught up in west-southwesterly flow ahead of an approaching deep-layer trough that is currently located over the Great Lakes region, causing the cyclone to accelerate toward the east-northeast at forward speeds in excess of 30 kt by 36 h. The new track guidance remains in excellent agreement with cross-track differences of only about 60 nmi and speed differences of just a couple of knots. As a result, little change was made to the previous advisory track, and the new NHC forecast lies down the middle of the guidance envelope, close to the various consensus models. Little change in intensity is forecast during the next 36 h or so while Maria remains over SSTs of 26C-27C and the vertical shear is less than 10 kt. By 36 h and beyond, Maria will be moving over sub-25C SSTs, reaching 21 deg C water by 48 h. The colder water, along with increasing wind shear and dry mid-level humidity values of less than 40 percent, should induce some weakening. Maria is expected to become extratropical by 72 h due to these unfavorable dynamic and thermodynamic conditions. However, given the very cold water that will exist beneath the cyclone, it is possible that Maria could become extratropical as early as 48 h. The extratropical low is expected to be absorbed by a larger low or frontal system over the northeastern Atlantic by 96 h, before the low moves across Ireland. The intensity forecast remains in agreement with guidance provided by the NOAA Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 36.8N 69.3W 60 KT 70 MPH 12H 29/0000Z 36.9N 66.7W 55 KT 65 MPH 24H 29/1200Z 37.4N 62.1W 55 KT 65 MPH 36H 30/0000Z 38.8N 56.1W 55 KT 65 MPH 48H 30/1200Z 41.3N 48.8W 55 KT 65 MPH 72H 01/1200Z 47.9N 31.2W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 02/1200Z...DISSIPATED $$ Forecaster Stewart
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